06 Mega Cab 6 speed rpm in 6th gear?

[JohnJansen]

Hello

We have a 2006 3500 4x4 Mega Cab SRW. We factory ordered the truck specifically to get the 6 speed. Not sure if we made a mistake, now have 29,00 miles on the truck. Fuel mileage is 15 to 16 around town, occasional weekend trips with our 36 ft 5vr get mileage in the 9 to 11 range. Part of the problem (I think) is the overdrive in 6th gear is too low? I am turning 2,300 RPM at 70 mph. Still have the factory tires.

Anyone else have this RPM / mileage issue?

Suggestions?

 

[JoshKelly]

My father has an '06 Mega, 6 speed, 2500, 4x4, stock everything and regurally gets 19-21 mpg commuting to work. Now pulling his 26' travel trailer he gets around 15 mpg. The RPM sounds pretty close to what his is at that speed. Have you checked all the basics? Fuel and air filter? Have you checked all the fluids?

 

[AH64ID]

My dad has an 06 with the G56 and I have an 05 with the NV5600. . our mileage is pretty much the same, despite the huge rpm difference... So I doub't that's the issue... Driver style is the main cause in great or crappy mileage.



But yes, check the basics filters, fluids...



Even thou Florida is flat a 36' 5er isn't going to be light or easy to pull. .

 

[HBarlow]

Hello
We have a 2006 3500 4x4 Mega Cab SRW. We factory ordered the truck specifically to get the 6 speed. Not sure if we made a mistake, now have 29,00 miles on the truck. Fuel mileage is 15 to 16 around town, occasional weekend trips with our 36 ft 5vr get mileage in the 9 to 11 range. Part of the problem (I think) is the overdrive in 6th gear is too low? I am turning 2,300 RPM at 70 mph. Still have the factory tires.
Anyone else have this RPM / mileage issue?
Suggestions?

Early G-56 transmissions were probably lifted right out of the German box/delivery truck market and installed in late 2005 and early 2006 Dodge Rams.

IMO , they were simply geared too low for US highways and usage. I drove one before I ordered an '06 w/48RE. The gearing was changed later to provide slightly taller first and overdrive gears.

I agree, however, with the post above. Towing a 36' fifth wheel requires considerable horsepower which consumes fuel. The fuel mileage you mentioned is about what I would expect. If anything, the gear ratios in the early G-56 might actually be better for towing a fiver that large and heavy.

Pay no attention to the fuel island liars who tell you their truck gets 18-20 mpg while towing a trailer the size of yours. The laws of physics make it impossible to achieve that mileage when towing a trailer of that weight and square feet of frontal area.

 

[Regcabguy]

Dream,dream,dream.

I upgraded to a 285-75-17 tire which dropped my rpm's considerably,but caused me to lose 1 mpg. I'm glad I got the lower ratio because I planned on going with a 34" tire. With my constant camper load and wind resistance,I'm averaging 13. 5-14. 5 city/highway every tank. After owning a DTT auto on the 98. 5 CTD,the stock 48re wasn't going to cut it nor was a $4500 upgrade affordable. Rowing in the city gets old fast,but once it's on the road the simplicity is reassuring. If I had Jay Leno's income,a DTT equipped heavily bombed '07 CTD would be in the driveway also. Dream on.....

 

[SierraRam]

I had that same RPM with mine when new, after the lift and 37's it runs 2000RPM@70mph, still get the same mileage as you though do to the lift and tires.

 

[JBonpua]

Before I changed to 37" tires I had the same RPM you mentioned. However I cruise @ 60 MPH and the CTD turns right at 1,700 RPM with a 37" tires. I do routinely get 22. 45 (hand calculated and speedo corrected for 37" tires) MPG on the highway going 60 MPH.



To lower your cruising RPM you can either get a Gear Vendor or install a taller tires. I chose the cheaper tire option. The later G56 (I believe built December 06 or later) do have a taller OD 6th gear.

 

[HBarlow]

JohnJansen,

You don't want to install taller tires for two reasons. One, the larger sizes won't be Load Range E, will lack the weight carrying capacity, and will have softer, more flexible sidewalls. Not good for carrying heavy weight because they would generate heat in the sidewall and casing. Two, taller tires would contribute to squirming or wiggling under the loads you carry on the rear of your truck. Taller tires are used by the off-road crowd for driving over rocks, sand, and for the off-road look.

 

[macdaddy]

Correct

JohnJansen,



You don't want to install taller tires for two reasons. One, the larger sizes won't be Load Range E, will lack the weight carrying capacity, and will have softer, more flexible sidewalls. Not good for carrying heavy weight because they would generate heat in the sidewall and casing. Two, taller tires would contribute to squirming or wiggling under the loads you carry on the rear of your truck. Taller tires are used by the off-road crowd for driving over rocks, sand, and for the off-road look.

In addition to what HB mentioned, youll also be up to bat for KDW (Killer Death Wobble) and premature failure on all steering, suspension, and drivetrain components.



Mac

 

[AH64ID]

JohnJansen,



You don't want to install taller tires for two reasons. One, the larger sizes won't be Load Range E, will lack the weight carrying capacity, and will have softer, more flexible sidewalls. Not good for carrying heavy weight because they would generate heat in the sidewall and casing. Two, taller tires would contribute to squirming or wiggling under the loads you carry on the rear of your truck. Taller tires are used by the off-road crowd for driving over rocks, sand, and for the off-road look.

You can go up a size or so and get positive results. Like a Toyo 285/70/17 is a load range E, 80 psi, and holds 700lbs a tire more than the OEM tires... Its a better ride, but also seems more stable with a load...



Otherwise I agree. . stay clear of tires that won't allow 80psi, as most 285 and larger tires do.

 

[Forrest Nearing]

plenty of E rated tires out there... you want 37's in E rating? no sweat...



but, I would stick w the factory tire size... maybe go up to 285's as mentioned above when it's time to buy tires.



2300 is actually pretty much in the sweet spot for towing. I run 2500+ quite often in my truck.



fuel consumption is more a factor of wind resistance/speed and work being done, not RPM...



IE, lowering your cruising RPM to say 2000rpm at 70 might give you a slight increase in mileage, but not what you're hoping for.



I would put a Smarty Jr. programmer on it.



I picked up an honest, hand calculated 2mpg on my 06 when I put the Smarty on... When I drove it home, I got 14mpg (4hr drive from Dallas to Houston) Loaded the Smarty and got 16mpg on a 7hr trip the following week.



If you're wondering why my numbers are so low, I usually drive between 80-85mph

 

[SierraRam]

I agree that you heavy haulers don't want to run 37's. All though the weight rating of a d rated 37 come very close to a smaller e rated tire,



As far a death wobble you just need to lift the truck correctly an make sure the axle is correctly centered and the caster is correct. Yes larger tires have some squirm to them but my thruck handles very well. I do pull a boat or travel trailer and do not have any problems (both are less than 9000#).



All depnds on what you use your truck for.



I have done the economy run and stayed at 55mph and did pick up 2mpg (18. 5) but it killed me! I guess I am with Sammy Hagar "I cant drive 55!"

 

[Ereynolds72]

I'm pretty sure by now 3:42 ring and pinion gears are available for AAM axles if you wanted to swap.

 

[SBeretz]

I have the same setup, early G56 with 3. 73's. I ran for about 40K miles on the stock tires, and then when I replaced tires I went with the Toyo 285/75 OC AT. I don't think I gained anything for mileage and it dropped me about 100-150RPMS at 70MPH. I have since went back to the 265/70 and mileage is probably touch better and the responsiveness of the truck is better. I have a mild box on my truck and never had any issues with the larger tires pulling my 40ft Toy Hauler. I just didn't like how much taller the truck was once I hooked up the trailer. I couldn't make it level. If I were you, I would switch to 3. 42's and call it good. Yeah, it will probably cost a thousand bucks to do the swap, but you will gain mileage, and shouldn't have to worry about finding 5 tires. I didn't like the idea of maybe having to find a tire that was an odd size if something happened to my odder sized tires. Toyo's, Nitto, and that is about it as far as load range E tires that are meant for our truck in the 285/75's. The new trucks with 3. 42's and the 6 speed are geared about right for everything, they stay right around 2K RPM's and that will pull about any load you should have behind the Cummins. Mine runs about 2250 at 70. A little high, but I never have to come out of 6th gear. Scotty

 

[JCarlisle]

I have a 2005 3500 and regularly pull equipment and a big Dump Trailer I Gross anywhere from 14,400 to 26,000 lbs and the truck gets as low as 7. 5 mpg and I have gotten 21 mpg empty. It is stock except for an exhaust brake and a Muffler eliminator kit.

I would caution about pulling heavy loads without a pyrometer as my truck will go over 1500 degrees if ambient temp is low and I am pulling a 6 to 8% grade.

 

[SBeretz]

I don't actually know anybody that has a G56 and dislikes the transmission. I would imagine if you drive empty all the time, it would be a little annoying with the higher revving OD, but if you pull, the truck really shines and the gear spacing is excellent for me. I was a little worried when I ordered the G56, because there were a ton of stories about what a horrible transmission it was going to be, but it turns out to be the best manual transmission I have ever driven in a pickup. It would be hard to switch for the next truck, especially since the auto costs more, and you don't really gain anything but two OD's which one is only really useful for heavy loads. Scotty