Auto Trans-hard shift in and out of 1st gear - 06 S80

[markhaas42]

My 2006 S80 has 132K miles and lately it has been making a very rough shift in and out of first gear, but only when it is hot and has been subjected to a lot of stop and start "city" driving. It is tough to explain, but particularly on the downshift as you slow to, say, 10 MPH, when it shifts from second into first, you feel it far more than you should - a significant kick. The same thing occurs when you accelerate and it shifts from first into second. The obvious fear is a major transmission issue, but I wonder if a broken motor mount might be the issue, or maybe something else. If it is a transmission issue, might there be a treatment that doesn't involve total rebuilding or replacement? Filter clogged or something like that? I checked the fluid level and there may actually be too much fluid and I wonder if that could be the issue. Any feedback would be greatly appreciated.