Speedometer jumps around and will not shift into overdrive?

Howdy. So, my journey began a couple months ago all the suddenly, my speedometer wouldn't work at all, but I noticed as soon as I press the brakes it would kick on while I was running down the road. But this would stop if I slow down too much or was I had a complete stop. Then it would have to pump the brakes again a little to get it to work again. Also, overdrive would not work at all obviously unless the speedometer could read a certain speed. I called my friend who is an expert in almost literally everything, and he said it was most likely a speedometer sensor. Me and my buddy spent a few hours checking out speedometer sensor it was what seemed it was worn down, so we had the idea of redneck engineering it and putting a few spacers on the speedometer sensor to pull it away from the shaft that was rubbing on it grinding it down. That actually fixed it for a couple weeks. But then it began doing the same thing. So, after some consultation I determined it had to be the bearings in the transfer case and the shaft was wobbling getting closer and closer to speedometer sensor. Rather than replacing the bearings which would have required taking apart the transfer case and rebuilding it. I opted to get another transfer case that was guaranteed to work from a salvage yard. I proceeded to install the transfer case thinking it would fix all of my problems. But to my amazement all the same problems were occurring, speedometer going in and out, can't go into overdrive, brakes seem to pump it up a bit, and parking brake indicator is always on even though parking brake is not on. I'm at a complete loss as to what to do, especially since it came with a new speedometer sensor and everything else that comes with a new transfer case. What the heck is going on, please help me! Ha