I don't think I've ever been near 7k rpm in my LTG even no lift shifting... They are huffed by 5500 or so.
If the crate ECU is tuneable then that would probably be a good route that way you are starting with a cleaner slate. I've never personally done a reflash like I'm suggesting, in fact there is some debate on the transmission board as to whether or not it's possible... Everything I've read seems to indicate yes, it's possible. Sooner you get linked up with a competent tuner, the better as going down the wrong path gets expensive quickly.
AFAIK driving modes only change shifting parameters (raises RPM up shift/gear hold/down shift) throttle pedal sensitivity and possibly steering power assist
Off the top of my head, auto trans tune monitors input shaft speed, output shaft speed, gear, temperature, tq converter status just to name a few. Your gear spoofing may work if you can successfully disable all of the other dependancies. Your gear spoof is also very analog...
Does your sanctioning body allow this :
https://www.onedirt.com/features/ask...right-for-you/
Much faster and more granular then you grabbing a button and would save you from messing with the auto trans tune. If it's not allowed:
I'm sure it's on the interwebs somewhere but the stabilatrak>ECM control loop would be interesting to take a look at. Depending on how clever you are you may be able to pull off this same functionality with the stock ECM stability strategy (spark cut) with some wheel speed sensors