I can only report what I've found on my own truck and it may be due to other problems, but here's the result of my pondering gearing with respect to larger tires:

I have 33's on my truck and stock gears. I definitely notice that it feels like it's geared improperly for the tires. It's kind of like starting in 1.5th gear rather than 1st. Besides the issues with starting up, I believe that it also affects the gas mileage. Since the gears are effectively too high with the larger tires, I find myself one gear lower than I should be for the speed. This results in lower mileage. The alternative is to go up the gear, but then I lug the engine which isn't great either.

This is for road driving too. For off-road, the situation's worse. Even in 4-low, I find myself going faster and bouncing off the bumps harder than I prefer.

In short, if you are going to go with bigger tires, re-gear your diffs. I'll be doing that this spring I think. (money, job, etc. permitting)

Chip