hmm,
are you a "Streetracing" type because these sound like the symptoms of a tranny that has undergone a bit of drag-racing style starts.
do you know the history on the car? did the previous owner drive it HARD or race it?
failing ring an pinion possibly. does it sound like a box of rocks back there? the identical thing happend to my 924 tranny about 18 months ago and i know what killed it...
I DID!
obin