Truck would not down shift

[revflyr]

I have a 2009 3500 6sp auto with 3000 miles and I've had the same problem twice while towing a 16500# 5th wheel. On trips back from the ocean I go thru a area where I reduce speed from 60 to 40, at the end of this area there is a start of large hill. When I give it more throttle nothing happens, it will not down shift and it will lug up the hill at app. 45. The engine temp is reading app. 205 and will drop under 200 after getting to the top of the hill and everything starts working again. I have the truck in tow/hual mode with the jake on. Should I hear the cooling fan kick on, in my fords it would sound like a jet taking off when it would kick on? I will take the truck into the shop tomorrow but they are telling me it will be hard to find if I did not get a warning light to find the problem if it only happems under that kind of load. Has anyone else had a similar problem and what did you find.

Thanks

 

[HBarlow]

You've got the paddle shifter button on the shifter. Why don't you simply override the ECM/PCM and downshift it manually to get the engine speed up slightly?

My C&C w/Aisin transmission locks 6th gear/second OD out when in tow/haul mode so I don't experience that lugging situation when towing. My guess is the ECM/PCM are programmed to take advantage of the low rpm torque of the Cummins engine rather than downshift. Your engine is producting maximum torque of 650 ft. lbs. at only 1500 rpm. If the tach is dropping below that at the speed you're driving you can easily shift down with a flick of your right thumb and put the engine back up to 1800 rpm or more to pull the grade.

I'd make a large bet nothing is actually wrong with your truck and the techs won't be able to offer you any satisfaction.