33's will not void your warranty, nor do I believe 35s, but I have 37s and recently had problems with my automatic. 2007 Jeep JK Rubicon Unlimited, 4" lift and 37s. First/Reverse clucth rings were destroyed. I don't know how... just bought it built and drove it from California to Texas... ~1400miles... Half way through the trip I heard some noise which I thought was the rear differential as I just had them install the correct 5.13 gears for the 37s. Got to Texas and went to load it on my trailer for wheeling that weekend. Backing it out of the driveway and didn't come to complete stop prior to putting in drive... heard a pop and not forward momentum... thought it a driveshaft, but to my dismay... transmission. Grubbs Jeep (Screamin Lizards) would not warranty the tranny because of the 37s and the Jeep did not have 7,000 miles on it and I just drove it 1400 miles concerned with drive/OD, but there was no sign of overheating and the damage was to reverse/low. Grubbs said the previous owner must have done something... yet I was still able to drive 1400 miles. Not satisfied I wanted someone from Jeep... thus, a Jeep district rep came out and agreed with them... of course he did... wouldn't want Grubbs to have mud on their face. They wanted $3850 to replace it. I reference Screamin Lizards as they are part of Grubbs and routinely put on 33s and 35s as well as hemi conversions. Of course when I referenced that they said, "Well... Jeep doesn't warranty them, but Screamin Lizards does." With the district rep there they no longer made such distinction. Speaking with a different dealer (I selected the wrong one) he said he could probably cover it, but not that I took it to Grubbs... to late and even if I took it to him Grubbs would red flag it to Jeep. I suggest you have a second set of tires available if you run large... swap them out when you go to the dealer for service.