Transmission shifts

[zibsBenz]

94 s320 with 492,000Km. Trans has never been serviced, car was a gift with 190,000 Km at the time. Its never winter driven. Last year there were a couple of OD shifting instances but they seemeed to have disappeared, we never experienced any more issues. This year the trans is having shifting issues.
At start up cold or hot it has no problems going into reverse or first instantly, no hesation at all. Start off in 1st, upshifts quickly and smooth, then next gear a slight lag and it shifts and so on, sometimes into overdrive but overdrive shift is becoming more rare.
As the trans gets warmer the lag between 2nd and 3rd is about 20 sec's and into the next gear most times will not shift unless speed is increased and engine revs are at about 4000 plus Rpm and you let off the accelerator slightly at which time it will shift instantly or not for about 60sec's or so.
There is no problem in down shifts, when slowing down or stopping it finds its lower range.
When driving in overdrive which at times it does get, although more rare, you never know when it will downshift out of OD. It will bounce up and down, downshift and upshift never staying.
Today I checked the fluid level cold before startup and it showed far up above 80 deg mark. After startup it dropped to nearly nothing on the dipstick, I checked it several times, so I presummed it was low. I got a Litre of Dexron111 and put it in, checked the fluid and now its way above the 80 degree pt. farther than when cold check. I'm now it seams 1ltr plus overfull I don't understand this. Went for a drive and nothing different in shifting , fluid level way overfull.
Any thoughts.