So I have this problem with my transmission, that it goes back to park after second or two. I thought maybe the VB sleeve or solenoids are bad, so I have replaced solenoids and the sleeves, but the issue still there. But when filling up the transmission, I’ve noticed that when the car is running, it just spits the fluid out and doesn’t suck it to the torque converter as usually.

So my question, could it be transmission oil pump? I have no codes related to this, all I’m getting is only a code for the diff.

I had replaced my transmission from 6HP19Z to 6HP21 and drove like 100 miles, it started overheating, car engine just stalled, once I restarted my car, the transmission was acting as I described before.