In case this helps anyone, my car's transmission was starting to slip a bit. The other day, I went up a steep incline and it just revved really high without engaging.
I purchased the Wix 58618 filter kit (it came with filter, o-ring, and transmission pan gasket), 6 quarts of Royal Purple ATF, and 1 bottle of Lucas Transmission Fix.
I got about 4 quarts by draining, dropping pan, and replacing filter. I did a drain and fill with filter change about 3 years ago and haven't driven the car much since then. The pan had gunk on the bottom and fluid didn't look horrible but was a bit dark. Magnets seemed like they had a normal amount of shaving for 3-4 years. I couldn't get the transfer case plug out as I stripped it a bit. I put everything back in (put all the screws through the pan and gasket before putting back on) and pour 3 quarts of Royal Purple through dipstick hole. I then remove the hose from the cooler and pumped out about 3 quarts. I stopped when the color of the fluid changed and it started to sputter.
I put in another 3 quarts of Royal Purple plus the Lucas Fix (which has the consistency of honey). After test driving, the results were immediately noticeable. Shift were smoother, acceleration more precise, etc.
I'm not sure if it's because I change the filter, replace 6 quarts of ATF, or because of the Lucas but it seems to be working pretty well right now. I'll update in a few months.