well you can either A) get a tlok and the gears you want or B) find an 8.8 off of a GT and get the gears you want or even C) find an 8.8 that someone has already put gears in.
Keep in mind with any gear change you'll want a tune to fix the speedo. Since you're an auto i feel ya man on how it feels stock. although once it's tuned even with the stock rear that auto becomes a beast on a good tune. check out american muscle and either a bama chip or bama tuner. just depends on what you wanna spend and if you're gonna mod alot. if a lot save for a tuner. if like me and its just occasional then get the chip. also welcome to the site. hit 50 or so posts and AM will be nice enough to give you a nice discount code to help ya out