Put the last 7 digits of your VIN into realoem.com. It will tell you if you have an M50 (I am sure you have) and your transmission type (could be 1 of 3) which would be helpful. This information would also be useful:
Does the display in the cluster reflect what the lever and mode switch say? i.e. does it say E D or S 4 etc correctly?
Are your transmission oil cooler lines getting warm?
Have you checked the auto transmission fluid level? Any leaks?
Have you had a look underneath to see if the lever on the side of the transmission is actually moving freely and in time with the shift lever?
Does it say 'transprog' on the cluster by any chance?
Oct '00 E46 330i. Feb '92 525i (departed)