Audi 5000 turbo / 1986 + Trany Issues... ? HELP!!!!!

I have an FWD 3 spd. auto. The transmission has recently started to slip after driving... by this I mean, you leave for a journey, and after about
1-2 minutes, revs go up, but you don't move. If I set Gear shift to N or Park, then back to Drive, (Or 1 or 2), I hear the click engage and also the slack in the gearing being taken up , however upto 4000 revs, no motion of car moving at all. Same problem in reverse, however this is what I find interesting; If I set the gearshift to N or park after this has occurred, and turn off Ignition key, and 'Immeadtly' restart the engine, and pick D or R , it will drive again for 1-2 minutes before repeating this process over and over. Im this that this is a bad thing!. It does not seem likely that this is a case of overheating, as an instant restart will give the car full motion again.... more like an electronic or pressure issue in the transmission. Ive checked fluid level, and it is just over the 2nd dot now... No oil seems to be present, so I think that the gear old and tranny seal is ok. Does anyone have any ideas to check.. modulator, drop pan... Anything!
Thanks a lot for any info!
- Jonathan
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