Working on a customers LS2/4L60 (2006 GTO) swapped C4 Corvette.
While on the dyno doing a bit of part throttle fuel tuning got a p0700, looking at the log Trans Pressure mode goes into whatever "Diag Max" is and then limp.
Tried to recreate it, seems to happen in 4th usually when the converter is locking up.
I tested with the TCC PWM lock/unlock 'off', with it in the off position it did not code or go into limp mode.
The transmission was just rebuilt with a few light upgrades.