sounds like a bad transistor to me

but make sure you have all grounds to frame eliminated. you should have no more than 100,000 ohms resistance to frame from any component on the system. check the battery and make sure it isnt bleeding through to the frame as well, remove it from the truck and recheck operation. If you find grounds to the frame from any component repair those first then re-run your checks.
But all in all i think you'll find the one transistor partially shorted causing that voltage your seeing.

Also check your fwd/rev contactors , i've seen those cause issues like this before too. They may click but still not make good connection. Take them apart and check the contacts and replace them if they are burned, melted or pitted.