Make sure the harness connector to the transmission is clean. There are a lot of pins in that connector, and I was told it was not uncommon to find factory harnesses lacking di-electric sealing grease in those sockets. Mine looked like it was packed with mud when it was taken apart and it made the transmission act up like crazy.

2002 X5 3.0 236,000 miles
2004 325i 105,000 miles