Probably just me I hope, I tinkered with my throttle body sync plates, in my case it changed some voltage values that either supplied to much voltage or not enough, in turn would not allow my reverse ( the idle was at 1700 plus or minus and would not retard and stall when button held )to activate until I readjusted it. ( See TPS settings in shop Manuel )
Now having said that I should have never messed with it at all. The Shop Manuel tells us adjustments should never be made unless Digital Wrench tells you they are out of sync or if they have been tampered with.
Not sure if this is your case, however for me a lesson learned, I will take my sled in and have it re caliberated back to factory spec, as the Manuel states, severe damage may occur if the throttle plates are out of sync, I wont take that chance, FYI, get a Shop Manuel and read up on any part of this sled before tampering with any components, just my experience, research what others say, use the science and engineering that is already in place to understand your Sled before screwing with anything.