I was getting a code 42 after my T56 swap. Trans swap had nothing to do with it just when it happened. Chased wires for a couple hours with my meter and test light following the test tree for that code. Couldn't find anything and just as I'm about to pull the ignition module I discovered the 4 pin connector plug housing is cracked pretty good... Just to rule it out I de-pinned that plug from a spare wire harness and replaced the cracked one. Problem fixed instantly.

Sharing just to see if it helps someone else...