You're probably mostly worried about rear wheel torque. What gear ratio are you running? For that matter, what's the overall diameter of those tires? Sometimes the best mod for increasing torque is the final gear ratio. For example, if you regear from 3.08 to 4.11, you'll get a 33% increase in torque.
I would first find out what gears you have. If you still have the original gears that came from the factory, you can look on your RPO code list in the glove box and look up the code (look for a Gxx code) in any of the RPO code lists on the internet. If you're not certain if you have the original gears, you'll have to either open the differential and count the teeth on the ring and pinion (gear ratio = # teeth on the ring gear/# teeth on the pinion gear) or count rotations of the driveshaft per rotation of the tires.
You can buy R&P's through many parts stores, or on-line retailers. Put differential ring and pinion into your favorite search engine and you shouldn't have any trouble finding vendors. If you decide to consider this seriously, you might consult with whoever will be doing the installation as to where he/she gets them. I'm guessing from your question that you've never worked much inside a diff, and setting up gears is not a job for a novice or the faint of heart.
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