TH350 Not engaging in drive.
So heres my problem. Put a Th350 in my 61 on pickup, It was one I picked up at a swap meet supposedly had only about 18000 miles on rebuild a cursory inspection led me to believe it was ok. For about the first week or so it ran fine, go solid shifts, no leakage, no abnormal noises. then today while driving it just started slippage, engine revved up but transmission was not engaging, roled to a stop shifted to Park then to reverse nothing, same when shifting to drive. Killed the engine then restarted it, would shift into reverse and drive but seemed very soft moved forward some more and then the same problem. Parked it and let it sit and cool down for a while, when i came back and restarted it it shifted and drove like normal for a while then the same problem. I thought i might have over filled it so drained some fluid started let it get up to operating temp and carefully topped it off again. took it out again and again the same thing, though this after shifting into drive a little more rpms would engage first gear but it would not upshift into 2 and seemed to be sliping. After this latest trial a checked the fluid in park and it showed way way high on the dipstick.
When i got it i did change the fluid and fliter in the pan, the fluid is still pink and non-smoky.
Im at a lost, im pretty smart but i don't have a lot of experience with auto trans so input on where to start would be great thanks I really appreicate it.