my 300 TD has about 380,000 miles. It goes into 2nd and third fine, about 5 mph later than the marks on the spedometer, no slipage, but sometimes the shifts are delayed, like 3rd happens closer to 50 MPH.... Never 4th gear.

Ive gone as much as 80 MPH and RPMS only climb 3500, 4000...

Incidentally, when I turn the car off theres a noise on the driver side, like air escaping that goes away in a minute, I figure is a vacume leak...

would that be the cause, or what other possibilities?

I just bought the car and for me its always been this way. Should I just figure "bad tranny" and resell the car?

Thanks