So I pulled the transmission to reinstall the original flexplate, reinstalled everything, and now I can't get any torque through the transmission in any gear.
After putting it back together, I filled it with 2 gallons of ATF, started it and had the return line in a bucket to try and do a little flush while I was at it.
It did fill the bucket slowly while I rowed the gears; I got a couple gallons but it took 5-10 minutes. And it seemed to flow more consistently in park than anywhere else, which seems to be exactly backwards of what it should be?
It did suck down the fluid though, so I put in another ~5 quarts and reconnected the return line.
Then I continued running the thing through gears, for around 15 minutes probably. Long periods in park and neutral. The ATF level stabilized right at the top of the SAFE mark in neutral.
Then I overfilled it by three quarts to see if that'd make a difference. I continued to run through gears for another 10 minutes or so. I saw the fluid level stabilize again, this time to the "N" in "check fluid level while idliNg..."
Absolutely no torque to the wheels at any point during the ordeal.
I do have the linkage connected. I have at least confirmed that it engages and disengages the parking pawl when I go in and out of park.
My temperature gauge in the hotline never got above 100 F.
Please help me.