Not sure which brake switch setup his truck had from the factory as GM switched to a single brake switch on the newer models, but both setups have a 12V output that is switched off when the brake is...

You should be able to bypass the VSSB aka dRAC and use the speed signal output from the LT1 PCM to feed your RWABS and the Cruise. The LT1 cars and Vortec trucks use the PCM the same way that older...

My guess is the PCM is looking for +12VDC from the cruise control brake switch to some pin to activate lockup. The stock TBI PCMs use the same input to lock the converter. Without 12 volts supplied...