Had my truck on a scale a couple nights ago with a couple people in it. Fuel tank was just above 1/2, which holds 44 gallons when full. Tipped the scale at 10,260 lbs. Got my best fuel economy ever in June driving from Jackson, WY to Missoula, MT and had almost 1/4 tank left. Mileage was an astonishing 19 mpg on B20.
Most of my driving had been under 45 mph through Grand Teton National Park and Yellowstone National Park. I thought it was my speed that made the majority of the difference, but realized later it was mostly my boost.
I then tried to keep my boost at 0. 0 or under 1 psi, which meant my speed generally stayed under 60 mph. My next tank was over 18, the following 17. 25, then just 15 mpg. I've not only been driving faster on shorter trips, but also using air conditioning on a regular basis. I have 3. 73 gears. I would previously average 13 in the city and had previously seen a best of 16 mpg.
Just before the record breaking mileage I made 17 mpg while driving 85 mph from Washington, across Idaho, Utah, and into Wyoming. Go figure. I find his mileage claims to be remarkable and very hard to believe. A crew cab is a big truck! And he has 35s with 4:10s compared to my 37s and 3. 73s so he's turning higher RPMs than mine and from testing with my truck, I'm certain my mileage is better at lower RPMs and less boost. I see about 7 psi on the flat at 85 mph. Doesn't run a lot of boost cruising.
Even if he's swapped in a 700R4 or 4L80 those numbers are hard to believe. Makes me curious about how he has his engine tuned. With mine, the more power it makes, the better the fuel economy. I haven't refilled my 7 gallon water injection tank with windshield washer fluid lately so there is likely a causal relationship for my recent drastic drop in mileage. Same fueling station last 3 fill ups. Looking forward to seeing how I do pulling my 31' enclosed trailer.
Attention: TDR Forum Junkies 
