I do allot of towing a 21 ft camper my 04 5.7 2wd is no issue I was wondering about stepping the gears down to get better mileage has 3.92 gear in it now have read the 2 door 4.7 has a smaller gear in it anyone have any experience with this swap. Don't care about get up and go I know it will loose some just wondering what truck I can get the rear out of and will the speed sensor be the same.

 

I went from 3.92 to 4.56, so I went the opposite direction.
There's plenty of aftermarket options, as well as swaps. You could find a whole rear 2500 axle with 3.73 and swap that in, or just buy after market gears.

Gear ratio was not dependent on engine, but as preference.