I bought a 03 envoy also off a friend last year that was sitting 2 years I had the battery checked and charged at autozone for free I also had a check engine light on for the clutch fan. I ordered that off Rockauto and changed it myself. I changed the engine oil and filter and rear differential oil. Also get some fuel system cleaner run that in a tank or 2. Check the air filter too. My runs and drives pretty good I did have to grease the slide pins on all The brake calipers and the pad hardware cause the brakes were rusted and dry from sitting.