So I got my code reader and found that I hadn't been doing my KOER tests correctly. As soon as I started doing them correctly, 111 all pass codes.

As a shot in the dark, I texted the guy from craigslist that I got my tailgate from. Turns out he's got 3 instrument clusters from 93, 94, & 96. The 94 had the lowest miles on it, bought it for $40, and viola, everything is fixed.

The speedo still waivers a little past 50 mph, but not nearly as terrible as it had been. I'll be resetting the PSOM to my tire size as well, seems I'm running about 2/10s over every 6 miles.

Best part is, my truck now only reads 116k instead of 131k (not a huge difference, I know, but less miles all the same!)

Thank you guys for all the help!