bought my truck new,always the same milage 17 mpg at 60 mph,15 mpg at 70 mpg that is with 4:10 gears,we have to remember weight and wind resistance are not on our side,It is a truck!

 

as aerodynamic as a brick

 

its normal to get slightly worse economy during the winter but its more the truck then the fuel. you are not efficient with a cold engine and cold oil. the fact that the truck is running longer at colder operating temps is the bigger factor during the winter.

 

very good point coonhunterjoe everything on the truck requires more force to turn when cold.

 

ya, but when you have a warm running truck, cold air will help. i forgot about winterized fuel...

 

4.10 down to 3.55 may requier a carrier change. You'll need a micrometer to measure backlash, setup bearings to get the shimming right,and a air wrench that can run up to 500 ft lbs pretty easy and a shop press to press on the carrier bearings. Setting up the gears is the toughest. There are shims on the pinion shaft and the carrier bearings. These have to be spaced correctly for optimal pinion depth and gerar meshing. I've created setup bearings for Dana44/60/70 and Ford 8.8. The 10.25 will be next on my list. The setup bearings are old bearings that I've ground down a bit to fit on the carrier without having to press them on and off. I get the pinion depth and gear mesh right, then I press on the new bearings with the correct shimming on them.

Bob