When you install the gears it's a good idea to rebuild the T-loc while you are in there. Get a T-loc rebuild kit from Holcomb. Also, if you go to Ford and pick up an F-150 S-spring for the T-loc. It's beefier and will hold the clutch packs together better. There's a lot of useful info in this article for what to buy when rebuilding the rear end...
http://www.corral.net/tech/drivetrain/gears.html
I'd suggest you read that before installing the gears even if you have someone else doing the work.
Pulleys would be good for the next mod, but I'd do headers and a crossover first. Go with long tubes and an off-road X-pipe or H-pipe if you don't have emissions testing.
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