Are you using the tow haul mode and what gear ratio do you have? Most likely you have 3.73s; changing to 4.10s would help you out but be sure you change front and rear. They have to match or you will burn up your transfer case assuming its 4wd. You other option would be programming. Custom tuning will give you the most gains but there are also a few pretty good hand help tuners. I have heard good things about Black Bear Performance. Diablo Sport tuners are also supposed to be top of the line and I know you can increase tranny line pressure and change shift points with them.
Sit down for a few hours and use google. It is your friend and there are tons of forums and discussions on these topics.