Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
What you describe sounds like a spark plug, or ingnition coil issue. To get headed in the right direction we'll need to know what trouble code is triggering in the system. For that, you'll need to take it somewhere and have it scanned. Most parts stores will do that for free.
How many miles do you have on your Envoy?
Do you know if the spark plugs have ever been changed?
Were ACDelco plugs used?
Do you think you'll be able to get it scanned?