Depends on the tranny. Some automatics just don't like 35" tires, especially with 3.55 gears. Manuals make handle it better, with the lower first gears and the overall heavier construction.
3.55 are a bit steep for 35" tires. You'll want steeper gears just to gain back the torque your going to lose going to the taller tire.
4.10 should be your minimum choice. I know many people with 4.56s and 35s, and their happy. Some want to go even lower, though.
I'm running 35s with 3.92 gears, and not happy, even with as much low-end torque as the Dodge 360 V8 cranks out compared to other V8s. The difference between the stock 31-32s and the current 35s is amazing.
When you're going up hills, esp. with an automatic, you find the tranny will want to "hunt" if your gears aren't low enough.
Basically, it depends on the truck. With a newer Chevy (99+), I'd go with MUCH lower gears, they just don't have any low-torque. Lots of HP, but no torque down low.
Dodge Ram? I'd go with 3.92s at a minimum for a 360 V8, 4.56s for the 5.2 (318) V8, the 5.2 (as JasonB can tell you) just doesn't have the grunt to push a full-size dodge through 3.55 gears and 35" tires.
Now, one thing you should really keep in mind is that if you're going to be off-roading it, then you probably want low (numerically high) gears anyway. The extra control you get from low gears is surprising. Much more control on hills, "stair-climbs", and most importantly: going downhill.
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