Problem again with 722.3 after rear pump seal
 

I destroyed my last transmission after not setting the axial support screw back horizontal. I replaced it with a sun valley rebuild and a few months ago same seal was leaking...

I replaced the seal and the axial support screw is horizontal, however I drove today for 5 miles and it was losing gears. At a stop light it shifted into 1st, took longer to upshift, dropped out of 4th to 3rd. I immediately pulled over and checked fluid - a tad low but only a few mm below low mark.

I'm seriously concerned about it again and I don't want to destroy this transmission the same way.

Is there something I am missing here? Or can a few mm low cause this?
Edit: I replaced both fluid and filter when I did the pump seal.