auto box slipping?

[ash_a8]

hi i just got a a8 and the box has been fine had few other issues with electrics it had oil light abs light and no rev counter but went back in garage and they cleaned the connections up i take it and was perfect also when i took the key out the ignition come on not properly but did until opened the door then went straight of but that was sorted as well so that only left the washer fluid warning due to broken washer jet so i fixed that so it now had no warning lights so i thought great took the car for a run then all or a sudden it just started revving and no gears let the revs come down and it would cruise slowly, so got it home, the next morning i went out did the same but when it does it on the display where it says prnd234 ect was highlighted and doesnt tell you what gear its in, it then will slip but some times can start it up and doesnt then it does i can put it in triptronic but still doesn't tell you what gear you in all the time but can normally get it into 1st and drive it but soon as it goes up the gears it seems to start it hasn't had any problems before this
when i spoke to the garage i got it off they said there is a sensor that is realy bad behind the drivers side wheel but looks more like a abs but i don't know they said its to do with gearbox loom, it seems to be when it rained as well but might be a coincident

any help would be great before car is sold as spares its a 1996 3.7 sport