My money is on electric seat position adjustment. Don't know if it's a common problem with GCs, but my Toyota ('86) had that problem, and friend's '03 Envoy is doing it also. Found the culprit in the Toyota (pinched wire under seat). Can't determine the Envoy issue with seat yet, as she lives 1-1/2 hours away, but disconnecting seat harness under driver's seat eliminates battery drain.