Vehicle: 1990 740GL Wagon, RWD, B230F engine, AW70L automatic transmission, 207,000 miles on engine.

Replaced: transmission ($300 used, 165,000 miles on it from a 1989 that was in an accident), both motor mounts, transmission mount, used transmission has had a complete fluid change (including torque converter), also checked metal screen filter after removing pan but it was clean.

Problem: This problem is worse after driving the car for at least 10 minutes. When everything is cold it is not much of a problem. But after driving car for 10 minutes (and everything is warmed up nice), all forward gears will still work pretty good, but when I come to a stop and put it into reverse it takes 2 or 3 seconds for reverse to engage (a big nuisance when parallel parking in traffic!). I can press the gas pedal slightly to speed things up (which makes the coming clunk more severe). After some vibration there is a clunk and big jolt somewhere in the rear end. It's like the car is "thinking" about whether or not it "feels" like going into reverse, and when I give it some gas it acts like it is getting "mad" as me and then with a big CLUNK it BANGS into reverse! Reverse will finally be fully engaged at this time and work fine until I try to put it into reverse again and then the same thing will happen:
Hesitation to engage in reverse accompanied by slight shuddering and vibration then finally ending with a clunk which indicates that it is fully engaged in reverse. I don't know if this is a transmission or drivetrain problem or both. Can anyone out there please help me?