So you constantly turn down suggestions to go a B15 citing "too expensive" then you proceed to go full retard and go 6 speed.........A setup that costs almost 4 times as much than going with a B15?!?! :smh:
The B15 isn't bulletproof by any means, but if SE-Rican can run 9s on a B13 "glass" gearbox, you can get away with running a B15............if you fix your wheelhop issues ofcourse
I wish I had a better suggestion than checking mounts and bushings. However, from my experience (and although you have mentioned otherwise), sometimes tires can also pose an issue. Example: Street tires have a much stiffer sideway, meaning less compliance. Than limited compliance can translate into terrible wheelhop issues. They are also not a fan of drivetrain shock.
Tought to diagnose your issue over the computer unfortunately