on a 3800 w/ 4t65e swap, match years of tranny and engine PCM. The various years and uses of 4t65e transmissions have different connections. ie the round connector of the transmission. The 2000 Pontiac use transmission has an external shift position switch, the 2001 Chevy use has an internal shift position switch. So, the connector pin out is different. you can adapt the transmissions to the PCM, but if you start with a match, you won't have to adapt it.
also, for a manual to auto conversion, you will need:
Transmission cooler lines
shifter and shifter plate
auto mount brackets (mounts are the same)
flexplate (if your engine doesn't have one)
park position lockout detent cable from shifter to ignition switch (if you want the park lock out safety feature, without this, you will be able to remove your key with the transmission in any shift position. also, you will be able to shift it without a key in the ignition.)
automatic ignition switch (if you want to use the park lock out)
steering column (if you don't want the manual key release)
I did a duke w/ 5 speed to 3800 w/ 4t65e swap.
I didn't bother to swap the steering column or add in the detent cable.
I just have to remember to put it in park.
also, I used a 2000 engine from a Pontiac GP and a 2001 4t65e-hd tranny from a police impala.
I had to convert the tranny internal wiring harness to work with my PCM.
[This message has been edited by IFLYR22 (edited 10-19-2007).]