Could someone give me some real-world experience between 3.31 gears and 3.55 gears for mileage and towing? Looking into a new Power Stroke and all my research points to 3.55, but they are harder to find as the 3.31 is the default gearset.
Yes. 249K on my ‘11 6.7L w/3:31’s.
Running empty w/milder tires @ 80 on the GPS w/the cruise set (speedometer says 84, GOS says 80): 15-18 MPG depending on wind. For every 5MPH you slow down, you can add roughly 1-1.5MPG. Go from milder AT’s to more aggressive or MT’s and you’ll give away 1.5-2.5MPG.
Pulling an 18.5’ glass boat @ the same speed, 9-12 depending on wind.
I pulled a 24’ long 8’ tall bumper hitch a couple weeks ago from Fargo to Devils. I got 9 MPG running 80MPH on ‘29 and 75MPG on ‘2.
I have a 38’ ~10k# bumper-hitch camper I pulled from S of St Cloud to Devils Lake. No issue at all w/power. I made that trip @ 75MPH and got ~9MPG. My buddy bought the same camper a couple years later and I pulled it from Detroit Lakes to Devils and it did the same.
I helped a buddy move from Omaha to Bismarck. We packed his Honda Accord and my pickup full of his stuff and put the Accord on a heavy 24’ deckover I borrowed. I ran 80 and it shifted out of 6th once a bit south of Sioux Falls. I can’t recall MPG but I do recall running into a very stiff headwind from Omaha to Fargo and power was never a problem.
My 6.7L is an early 400HP/800Tq, the newer ones are 450-500HP and 1050-1200 Ft-Lb of Tq @ 1600 RPM, right where your running for RPM @ 65-70MPH. I’m not sure what you’d have to hook to any of them for the rear end gearing to actually matter. I’m sure there’s something, obviously they’ll tow much heavier than I have w/mine.
The newer models w/10-spd are supposed to get better mileage, mine has the 6-spd. Most of my towing has been on flat ground on I29, I-94, Hwy 2. It’s less than a half-dozen times the transmission has shifted out of 6th gear when pulling, and it’s never come out of 6th running empty at any speed w/the cruise set in any terrain. Hills, mountains, strong winds, etc, running empty it holds top gear and just adjusts boost as needed.
What are you pulling and what are you currently pulling it with?