I have a 1989 560 sel that, when cold, shifts as it should. I was on I-95 today, in Florida and I was doing 70 when all of the sudden, it shifted down to 3rd for no reason. I put it in neutral and reved the engine, then shifted it back into drive, and all was well for about 30 seconds, then the same thing happened. I got off on the exit that I needed to and continued to drive at about 50 mph and then it shifted on its own to 2nd. I put it in neutral and reved the engine and then put it back into drive and it went in to 4th again, but only for a short period and then shifted down to 3rd and then down to second. Mind you that when it did this, the economy guage stayed pegged to the left indicating that it was getting "great" fuel economy, but that is not true. Do you think that my problem could be as simple as a vaccum leak? Or is it something more serious? Any thoughts or opinions would be greatly appreciated! Thanks in advance!