Couple of Related problems (maybe)

[Jack Bobaganoosh]

I have an 01 Montana that I recently had the LIM replaced on. THe problem arose after reinstallation of the motor, I suddenly had a check engine light for 5 volt refrence (P0641) and the fuel tank always read empty. Here is what I have done so far:

1. Checked sending unit resistance at body connection. Checks good, normal range of resistance from near empty to full.

2. Checked Voltage at the MAP sensor. Reference voltage is supposed to be 5V, is currently 1.5. Can't seem to get the PCM pin to check wire continuity from the big connector to the alternatorto the PCM.

Is there a connection that has to be disconnected to pull the motor? The shop that did it is my brother in law's, and since they did the job for cost of parts, I don't want to make too big of a stink. I figured it might the the PCM, so I bought one on EBay, but whenever I went to replace it, there is this drawn out Passlock relearn thing that I can't seem to get right. I am on the verge of taking it to the dealer to have them troubleshoot it, and we can't have that!

Thanks in advance!