Have a boosted b20 fired it up after engine swap and revved it without axles in to try and engage two step now when I drive the car under load when I hit 4200rpm the car goes into lwgat I would describe as two step. Any help is greatly appreciated.

 

turn off the two step and see if your 4200rpm rev limit no longer exists.

 

^^^ That

 

Like the others said, disable the two step. If that remedies the problem your speed sensor is probably going out/disconnected/etc.