I found someone local who is willing to help with the servo install, but he wanted me to get it diagnosed before I throw money at it. Many people have recommended Greenville Transmission Clinic to me. I went there this morning and they told me it has to be rebuilt. They showed me a piece of metal that was in the pan. they did confirm my belief that the transmission had been serviced in the past.
I do think the servos and solenoid pack are part of the problem, but I now think other things may also be wrong. It slips out of gear, but not when my foot is on the pedal. Going up a hill, it slammed back into gear very violently. That was kinda scary. They said it's skipping 2nd and that 2 and 5 are out. I was not aware of that being the case because I manually take-off in "2" to avoid the problem shifting from 1st. It's taking off is some gear and going through 3 of them. I am taking off in "2", manually shifting to "3", then to "D" and getting 3 gears out of that. I haven't started from dead stop in "D" in a while, so it could be behaving differently than I previously described.
They quoted me $2,200-$2,800 for a rebuild, and that includes correcting design flaws that the original transmission has. I'm considering that. I just got a decent job, but it'll be a couple of weeks before I start getting paid. Then, I'll just throw money at the problem.
Some people say it's not worth fixing. I'm not going to buy some ugly new car, Explorer or otherwise. It's insane how expensive a new car is that's nowhere near as nice as mine. I don't want FWD if I can help it. I might consider a 1990's Buick LeSabre or Park Avenue with the 3800, or maybe an AE101 Corolla with a 7AFE.
