Engine rev / gear change problem with 1996 cabriolet auto

[Audi-arrrrrgggh]

Hi guys. I've got a 'problem' with my automatic 1996 cabriolet . This is a problem which has been on and off for the last three / four months where the engine will sometimes rev to around 5000 revs before changing gear, also she seems to be a little sluggish at times with a feeling of lack of power and is pinking. I had an auto transmission fluid change done on tuesday just gone and they did say that the fluid they took out was very black and for a few days afterwards all seemed sweet but low and behold the high revving and sluggish feeling is back.
Does anyone know if my car has an auto transmission filter that I should get changed, or can anyone throw some light on the problem - or is it (as I suspect) simply that the auto box is fubar'd and I would do better driving her off a cliff :-/
Really hope someone can help, love the car, love driving her in the sun with my dogs in the back seat with the wind in their ears :-) Just at my wits end
If you need any more info let me know - thanks guys

edited to add :
The car has recently had an ecu and flywheel sensor put in as she broke down on me and just wouldn't start - it took the garage 8 weeks (!!!!!!!!) to find the problem / diagnose the problem and then they said that the ecu they put in to replace my one was also faulty and they still couldn't get it to work - the high revs was happening before the ecu was put in but the lack of power / sluggish along with the pinking has been since the ecu was changed - could the garage have failed to do all correct adjustments / timing ? I'm guessing that the high revs is a completely different issue to the sluggish / pinking but that's only a guess. Cheers again guys.

[Henry Andrew]

Hello I just recently bought my Audi a4 2.8 v6 convertible 2 weeks ago and I'm having the same problem did you manage to fix the problem? please could you advice me on what the problem is or was and a solution if possible its driving me nuts