Dropping the ratio(number) or putting in a higher gear will increase milage to a point until the engine can't turn the drive shaft if you go way high. That being said you have to remember the 5.7 has very low gears because is has the 6 speed tranny that has 2 over drive gears and even 4th gear is a 1:1 ratio, so you get a super low 1st to pull with but the 6 speed with 2 over drive gears is really giving you a high gear that most other trannys don't have.

Be careful if you plan on changing gears. I would not go much more that from the 4.30 on the towing to the 4.10 on the none towing package trucks.

Slowhogg..........