1989 750il tranamission problem

Just bought a very clean 89 750il. 160000 miles and have all the service records. The tranny when cold sounds like an empty power steering pump? It will go into gear but after it warms up it is done. Have checked the fluid and it is clean and full. Any thoughts on what it could be before I pull it out? When it is warm and you give it some rpms a message comes accross the cluster about the transmission and says check the owners manual. I did find out looking through all the service records that in 98 the owner had 2 dinan chips installed for the engine and 1 installed for the transmission. That was at 143000 miles. Any help would be great.
Thanks..

Sent from my PC36100 using Bimmer App

check the pump in the torque converter
The chipset has nothing to do with it.

I got under the car and took the tranny pan and filter off. Filter was nasty. You could tell nothing had been done with the tranny for a long time. Is the pump you are talking about between the bellhousing and the tranny? Not sure where this pump is you are talking about. Have been looking online and cant seem to find out to much info on this.

Thanks