If you are a V6 2wd auto, there are two diff ratios that you may have. 3.7's if you had 225/75 tires, or 4.1's if you got the 265/70 tires.
If you got the 3.7 diff gears, then I think you will want to move up to at least 4.1's (or higher) with 33" tires. Other wise you will notice a big reduction in fuel economy and torque at the wheels.
If you got the 4.1 diff gears you should be ok with 33's but will again see a drop in milage.
My vehicle id labels indicate I have 3.9 diffs on my 4wd auto, but I got it with the 265/70 tires which means the diffs should have been upgraded to 4.1's. I haven't officially worked out what I have yet, but with the 265/75 (32's) that I have on now, I am not totally satisfied with the ratios, especially off road, so I will get some 4.3's soon.