x2 on the gears. Changing to 4.56s will get you an honest to goodness 10% more torque to the road. Should be easy to find used ones, or if doing lockers, that is a good time to install the gears.

I did some mild performance work on my 22RE with good results:
- http://www.4crawler.com/4x4/CheapTricks/EngineMods/index.shtml

At the bottom of that page are some subjective performance increases.

Also, if running 31s only, you could loose all or part of the lift and the lessened frontal area will help as well, less drag and better top speed and gas mileage (gears will also help mileage). I probably lost 10-20% fuel mileage in going from ~stock to 33" tires and my current lift.