[MDY]

black wall st - do a search in this forum and Jimmy (Envoy & Jimmy have the same stuff). Could be 4 things, TCM, Vacume Lines, Vacume under battery or solinoid up front under hood. Pull fuse or disconnect battery for 10 minutes and reconnect and try. My wifes 2000 envoy was stuck in 4 Lo last month, couldn't get out.. Take her to work, call tow truck to take to dealer, dealer calls "whats wrong". Tow driver got it out of 4Lo. Go figure.

Works fine now. (knock on wood). I feel your pain with this ride.