no you dont need to change axles. just ring and pinion gears.
if you know how to drive 33s will be fine. Tire size does not replace skill.
vortec said:i agree 100%. i get plenty done with open diffs and 31's. in fact, going to a larger tire than your engine or gearing can handle well will work against you, regardless of how good you are. that 1" extra clearance won't get you over that ledge. a more aggressive appearance won't help you plow through that mud puddle. i'm about to put 33x12.5 and a 4 lift on mine, and it's hard to make myself stay away from 35x12.5, for looks. but, 33" will be better for what i do and that's what's important for me.
also, one thing that many people overlook is the brakes. larger tires mean more stress and heat. makes a big difference on hill descents.
Im using 39.5 inch tires with a 4inch lift

Mreetz said:I installed a 4" lift, put on some 35s, blew up my stock 10bolt, installed a 12bolt, blew that up, replaced both axles--went to 4:10s and a 14bolt....goin to 38x14.5s next week!!
LOLThunder said:33s or 35s 6 of one half dozen of the other. Dont listen th the guys that say bigger is better. I mean what are you talking about 1, maby 1.5 stinking inch??? Frankly i preferr 33s with 3.73 or lower.
Jees if you know how to drive 33s will be fine. Tire size does not replace skill.
I'm not, but if you are aggressive offroad then you might want to save your fenders and go with 33's