Yeah, speedo a few percent high vs. VSS is how they have always been set up on the few GM vehicles I've played with. I think as long as the speedometer/odometer/cruise/instant economy work properly (i.e. they use the speedo offset number and not the VSS number), using that workaround doesn't bother me too much. I probably won't have time to mess with that for a bit but will report back on what I find.

I think I actually do have his email - I got the 0411 wiring harness file for one of my GMT400s from him so will try that route. You are right, never hurts to ask.

I know we're in the trans tuning section, but looking at other 8.1 files I did find it interesting that the early 8.1s with the higher ratings (pre-'04) have a higher VE table across the board by around 3% for most of the map and around 8% around WOT. That's a huge drop in fueling for the late 8.1s considering there isn't any documented VE-impacting hardware change that I can find in those years. EGR has its own modifier tables for when it is active.