82 300D new to me, runs great when cold, but when it gets hot the transmission seems to go out of gear, especially if i step on it in the higher gears.

It was a bit low on ATF, so i added some gradually, and hard to tell, but it may be slightly over full now. IN ANY CASE, ATF LEVEL MADE NO DIFFERENCE.

Usually if i let up on the diesel pedal, it will pop back in, sometimes rather abruptly.

I was thinking of changing the fluid and filter, but since it climbs right up my steep driveway when cold, i'm thinking that ain't it, as another 300D used to have to warm up forever until the tranny would kick in, and that one did benefit from a fluid and filter change.

Wondering if the tranny is shot, or some adjustment is needed.

Thanks!