What is the best gears to have with 31 inch tires and the 4 speed tranny.

 

Here's my two cents' worth, (which is probably about two cents):
I've got 3.30 gears in mine, and I also have 31" tires and a 4 speed. For what I use the truck for, the gears seem about right. The speedometer is off quite a bit, though. At a true 65 mph, I'm turning 2300 rpm, which seems pretty comfortable, yet I've got enough low-end grunt to pull my boat up a fairly steep grade without downshifting. The overall gas mileage is good. For what I use my truck for, I wouldn't want to gear higher or lower, since I'd be losing one end or the other.