Ok guys....I just got my envoy a few months ago, so I'm not too familiar with the engine, etc. I'v been reading on here that if you go up to a 3" exhuast that you need to get a retune. I'v also been told that the stock exhaust size is 2.75". Is a 1/4" really going to make that much of a difference? What is it with the envoy that requires a tune when you go up to a 3" system? Does it run too lean? If this has already been explained, i'll gladly read the link to it. Thanks....oh and if it does need a retune, is there a program that allows you to do it yourself, and if not, whats the most common place people turn to?