2004 Envoy bad gas mileage, help

I have a 2004 Envoy, that gets 11/13 mpg, when we got it a couple years ago it got around 20mpg, it just keeps getting worse. I have replaced spark plugs, A/C pump, air filter, brakes, tires, Changed to full synthetic oil, both O2 sensors and even took out the cat I use fuel additives also. I have had it into 4 different mechanics, 2 GM and 2 back yard mechanics. No one can tell me what it wrong. not sure what to do next, short of replacing the engine or the whole SUV.

First of all the cat should be reinstalled. This can be a serious violation, plus it is under warranty for 7/70. Second only seeing the results of a full scan would help diagnose this, plus all the history, any tires replaced any history or previous cel codes? Change in route or driving habits? 4wd or 2wd? There is no quick answer here, only site diagnostics will help.

Are you using gasoline w/10% ethanol? have seen a slight decrease in mileage with this. Citgo, Valero.
Toyota posted a dealeship campain to stay away from these fuels.
Food for thought!

I seems all the gas in NYS has 10%.

I sure hope not. If they do it has to be published on the pump. I have'nt seen this on HESS or Kwick fill or GULF.
I hope these guys aren't pulling our leg.

I live in the Lk George area, I have not seen any pumps from NYC to Albany to upstate that are not ethanol marked, small tag, but it was there. BTW you may loose about 1 mpg using e10. If the pumps in Mich are not marked, which the feds require, than it is not e10.

Just wanted to run my situation by you maybe get some reply's. I have a 2004 Envoy 6 cyl 4x4 that I purchased used in 06. This thing gets 11 mpg always whether I'm pulling a trailer uphill with the A/C on or coasting in neutral. We've had it at 3 dealers GM claims nothing is wrong they don't get very good mileage! There is no way they'd of sold any of these with with the same mpg as a 71' big block Ford Camper Special!:headshake I love the thing but have wasted thou$ands of dollars because I went against my gut and opted for the GMC instead of the 4Runner. Also does anyone know what "Big Baller Edition" means? It's a a factory decal on back glass.:confused: Thanx in advance for any replies on this issue.
Dan

Welcome to AF. In the future start a new thread this is too old. That label is some kind of dealer package? What gear ratio do you have ,the codes are in the glove box, but no matter 11 is way too low, My 2002 averaged about 16.5 mixed and best on the hway about 20.5. Many things can cause poor mileage, short trips are the worst case, bad o2 sensor, dirty injectors, a full scan is in order here