You can go with either 4:10, 4:30, or 4:56 gears.
4:56 gears will give you the most of the three on the low end, but you'll run at higher RPM on the highway and your fuel mileage will suffer. 4:10 gears won't give as much of a low end response, but enough for you to see an improvement, and you'll be more efficient on the highway by running at lower RPM. 4:30 gears are the happy medium.
If you have a 7.5" rear end, you may have a hard time finding 4.30 gears though. Back when I regeared my 7.5, I couldn't find anyone that made them. That was several years ago though. I know they are available for the 8.8 rear.
Also keep in mind that changing the gear ratio in the rear will affect your speedometer. That can be addressed by buying a tuner, taking it to the dealer to have them flash your computer, or you can just run all of the calculations yourself and remember (or make a little sheet next to the gauge cluster) what speed you should be at for a given RPM and what gear the transmission is in. The latter is not really recommended, but it is free and it would work.