You should be using the Combo's BCM and not the SRi one. Problem I found was with my SRi and the Z20LET, if I turned off anything in the BCM, it cracked the sh1ts and spat out an error code in the BCM. I left everything as it was and it wasn't an issue.
Thing with the ABS+TC enabled BCM in the SRi, it has two sets of CAN wires going to it. One set is present in models without TC, but those with TC have two sets. If this second set isn't connected, nothing works properly, including your tacho and speedo.