Fixed it. It was the governor. A pivot pin on one of the governor flyweights had partially come off, causing only one flyweight to pivot and thus no governor valve movement at all. As a result, my tranny was shifting only on the vacuum modulator input. $20 bucks and 1 hour later, everything is just fine.
Now I just need to fix the leaks...
Thanks to everyone who gave input!
"...ridge reamer and ring compressor? Do they have tools like that?"