I have gone back and forth between 35's and 33's. I love the 35's but hate the need of the 6" lift, regear, etc. etc. I had 33's on my Tahoe and they were fine, BUT my Tahoe had 3.73 gears. I know it's a different vehicle than my 2010 Silverado so I don't know how much that throws into the equation. I have read that with 33's I should go to 4.10 gears. I looked at a couple of the gearing charts - couple of questions: 1 - when it says tire size does that mean pre-install or the actual tire diameter when on the truck under normal load ? I ask because on my Tahoe I had a Superchips programmer and they told me to measure the actual tire size under normal load to adjust for the tire change. Are the gearing charts the same way or do they mean the uninstalled full 33" size? I ask because if you look at the uninstalled tire size of my stock 265/65/18's it basically says my stock 3.42 gears are wrong. They have the highlighted for MPG/overall/towing but with stock tires and 3.42 gears I'm on the other side of MPG which gives no umph. 2 - Assuming the stock tire and gear is fine for overall - would a change from 31.5" to 33" make that much difference ? would just my tuner make up for it or would I still need to regear ? Sorry for the long post but I've been reading a lot and have thoroughly confused myself and need to be pointed in the right direction before I spend the money. I really appreciate it.