I recently acquired a nice s80 in good shape save the transmission. I knew this going in. I'm a mechanic so rebuilding or replacing it is not off the table at all.
However, if I can get it to behave that's obvious preferably.
1-2 shift is late and very rough.
2-3 shift involves a flare and settles into gear veeeeery slowly. If I let go of the gas and re-apply it helps it to "settle" more quickly. Up to 2500-3000rpm it holds ok but then quickly slips almost asif in N.
The 3-4 shift, when babied in is not as slow as the 2-3 shift. About 2/3 of the time it holds 4th fine, the heavier I'm accelerating the less likely it is to hold 4th gear. It will slip like it's in N but has a bit more "grip" than in 3rd. If I let off the gas and re-apply it holds 4th well and I can floor it and it holds (untill it downshifts in 3rd and slips like crazy).
3rd is the worst gear. 4th is inconsistent.
If I use Geartronic it holds and pulls well in 1st and 2nd (with a very late and hard shift) then into third is just not possible at anything pas half throttle, nor 4th.
The behaviour to me just isn't consistent with mechanical failure in my eyes. I just reset as much as I could using VIDA. When for a short drive, things are a little better but too soon to say. 3rd gear is not better.
I have no trans codes (had one relating to Engine RPM not matching trans RPM, the slipping)
The fluid is fresh and not burnt, although it's been replaced recently as this transmission was recently installed apparently. I've driven it about a week. I let off when it slips to avoid damage, but the fluid must be taking a beating but it's good.