e28 dead @ 2000 rpm

My first German car, a 1988 528e equipped with auto trans. It has 188354 miles on it at the time I bought it from a friend of mine, who bought it in1989. He didn’t want to sell it to me because of the fact it has some problems. I said to him, problems…I have been driving American and Japanese vehicles for 37 yrs. err let me rephrase that, I have been working on American and Japanese vehicles for 37 yrs.
Two months I worked on him to sell this car to me, as he poked around and bought this part and that, trying to fix it. Well it’s mine now, and here I am asking for help. The main problem (aside from the water leak in the trunk and a few burnt out bulbs) is a problem with how it runs, or fails to run properly after it reaches operating temp.
Here are the symptoms, runs fine cold, but after reaching operating temp.it cuts out at exactly 2000 RPM. (Almost like a rev limiter)This symptom occurs at any road speed or engine load. Runs fine under 2000 RPM, but soon has the tach hits 2000 RPM …WHAA…BOG…WHAA…BOG…WHAA…BOG If I mash the accelerator to the floor it seems like the engine returns to idle and the trans drops into neutral, let off the gas then every thing is fine. As long if I keep it below 2000 RPM.
I think this car has a lot of life left init, but below 2000 RPM, that’s not much of a life for me. Any guidance you can provide is greatly appreciated.

Talk about dead!............ Well I think what's wrong with my car, is something to do with RPM & heat.