3 times we replaced the tranny and reman them for an Alpina B12 5.0 E32, and still we had probs, here you can see why, torque converter
http://www.bimmerboard.com/forums/posts/538360

Now it runs fine and on the Alpina the lock-up is already from 2nd gear, not in last as usual.

Horsepower (HP/rpm) 350 / 5300
Torque (Nm/rpm) 470 / 4000
official data:
0-100km/h 6.9c
Top Speed 275km/h