It took longer than I expected to get around to this. If anyone is curious about the TUTD for the 6L80/90 you don't have to do a lot to get it working if you are doing a swap. Here's what you'll need to do:
1. Run a new wire
Parts:
Wire (18-20 awg)
Weatherpack/Metripack crimper:
Amazon
6L80/90 connector:
Mouser
Cable seal:
EFI Connection
GM didn't hardwire the TUTD. You'll need to add a connector and wire to the transmission harness. See this document from Speartech:
Speartech
2. Use a prebuilt switch, like this one:
Speartech
OR save yourself about $130 and do it yourself
Parts:
8.25k ohm 1% tolerance resistor:
Digi-key
4.42k ohm 1% tolerance resistor:
Digi-key
1.5k ohm 1% tolerance resistor:
Digi-key
Momentary rocker switch (anything will do here):
Digi-key
Wire it up according to the attached schematic. I'll let you decide if you want it all inline and clean or if you want to hot glue the components into the small box or something, but solder everything.
3. Retune your transmission:
You need to tell your computer you are running a 'Hardwire' TUTD, and setup the forced shift speeds. I used HPTuners. Also, these numbers are for a tall geared vehicle, setup your speeds for your vehicle. See the hptuners pictures.
I set mine to engage TUTD when the gear select is D4 (second position for my transmission), and a button press is detected.