if your only running 31's and dont plan on going up then 5:38's are going to be two steep, 4.62's are perfect for 31's. and then if u wanted u could do T-case gears for added crawl ratio,
the rest will make a difference, I run 2 inch exhaust, weber carb, KN airfilter on stock 1.3, running 31x10.5's all stock gearing and I can run 70mph easy. I do have 4.62's to go in tho...
all the stuff your running will make a difference, but like I said those gears are too steep for 31's and if u plan on running on road, if its just a trail rig, then u fine.
John