Just tonight, my 2001 Blazer suddenly went clunk, the engine revved up, and the whining started. I pulled into a shopping mall parking lot to look under the hood. After a few minutes, I discovered that I had no reverse. I proceeded to drive the 35 miles home, but I bet I will need a new transmission. Mine is a 4 wheel drive, and the indicator lights on the pushbutton switches have been intermittent for quite some time. I just recently had Valvoline Instant Oil Change do a total transmission fluid exchange; I hope they didn't do something wrong.