Ok....wow....so this is embarassing

Somehow it didn't come into my head to check the level of the transmission fluid. So I pulled out the stick while the engine was warm...completely dry

Went and bought 1 quart of ATF. I poured in half...still completely dry. Poured the rest...still dry.

Bought another bottle, poured half...just the tip of the stick was wet.

Ended up having to use almost the full two bottles of ATF before it was at the correct level on the dipstick.

Immediately the transmission started working perfectly.

Last week I ordered the K1 spring, along with the filter and transmission seal, so I'll do a transmission flush & replace the spring anyways when it all arrives

Hopefully I didn't damage the transmission