My truck got 19.6, hauling a KTM dirtbike to the north side of Indy this summer. Rain, construction, hills head wind, tailwind, 2 lane stop and go, highway.... . Just about everything. Tall gears equaling good gas mileage is an old fallacy that should be laid to rest.
At 55 mph with 4.10s, the truck turns the exact same rpm, because it now shifts into 6th at that speed rather than staying in 5th.
I remember those days that the truck was a real slug until about 20 mph. I used to say it was a six speed with no first gear. That super tall first gear in the 5/645RFE was another bad idea. You'll like that tranny a lot more once you get 4.10s. If you're going to be pulling 4 snowmobiles in an enclosed trailer, consider 4.56s.
