I don't have any complaints at all with my truck. I agree with shinerbock also. 5th gear in the 66 & 68rfe tranny is the unloaded overdrive. 5th is the loaded over drive. My truck pulls all day in 5th rarely downshifting unless passing hard or a long steep incline. I usually tow in regular drive, not tow haul, and lock out 6th. The Trans will sift into 6th on declines and with a tail wind when towing but shifts out easily so I prevent it from doing that. My only complaint about the 4.10's will come this winter when driving in the snow and ice. Rear tires break easy already on loose gravel or grass. In the snow and ice it will be worse. 4.10's are only available with limited slip added, that should help a little. I will rarely drive my truck in the winter though. If it's too bad to drive my car, I stay home.
I also run lower air pressure then the TPS was calibrated for. I had the dealer reprogram it the day I picked it up. I run 50 in the front 60 in the rear. I had the dealer set the TPS calibration to 50 psi at all 4 corners. When winter comes I will drop pressures to 50 all the way around. You can't compare the 6.4 to a diesel. If you are expecting diesel performance you will be disappointed. There are pros and cons of both engines. I'm my situation the gas engine was what I preferred.
