The updated manual valve and modifications/adjustment is more directed to allowing the transmission to fill the converter in park so unlikley it is casuing the problem but a good idea to set it according to the Transgo instructions.

From your first post, it sounds like the transmission was working fine before the install of the shift kit so logically the problem is somewhere in the vavle body or something done to the transmission during the install of that shift kit. I'd suggest going over each step of the install carefully including the band adjustment and also do some air checks of the clutches and servos while the VB is out.