Just picked up a 2006 GMC Envoy XL for a great price. It is in really good condition. I knew the guy who owned it. It has 185,000 miles on it, but has been babied, garage kept, and maintenance performed regularly on it. Just the usual brakes, oil change, air filter. Never had any issues from what he has told me. I have found out it doesnt do nearly as good on gas as my 2002 trailblazer did. I constantly averaged 22-23 mpg in my trailblazer. I have ran a couple tanks through the envoy, and Im only averaging around 14 mpg. The only differences between the envoy xl, and trailblazer I have beside the obvious size difference is....my trailblazer didnt have the spare tire underneath. It didnt have the big can muffler on the back I removed it. I cant imagine those 2 things doing much if anything at all for gas mileage. Do the Envoy XL's really suck that bad on gas, or is there anything I can do to increase it. Even if only slightly?