They are using the accumulator valve as the brake valve, it crosses into the torque signal circuit, actuator feed, and has reverse oil plumbed to it.
I think I have an idea what the issue is but I don't have a VB here to confirm.
I have everything working except reverse, and in reverse my pressure will sit at 75 psi, then spike to 250 psi, and then blow off. The result is a car that slams into and out of reverse.
I've built DOZENS of 4L80Es successfully for performance use, probably well over 1000 TH350s, Th400s, 200-4Rs, Glides, C4s, C6s, 727s, and even got to play with an A4LD the other day
I think the torque signal circuit and the way it is used by the solenoid is the issue but I'm not going to "R&D" the junk for him.
It has a design flaw period and he's passing it off as good.