Goofy downshifting, particularly when cold

[Ophidia]

'04 GT non-S/C. This has been gradually getting worse.

When the transmission is cold, it upshifts/downshifts fine. When it warms up, it tends to upshift very slowly on light throttle, and, when you're at a lower RPM in a gear and hit the gas a bit and it downshifts, it takes a very long time then almost seems to bang into gear. It's not the hard downshift feeling like when you step on it, more like a really slow shift then it just grabs and doesn't feel right. The car has 103,000 miles on it and I doubt it has had the tranny fluid changed. The level is good (actually a tiny bit high because I added some TransX, which had the expected lack of effect).

Does this sound like something is wrong, or do I just need to drop the pan/change the filter?

Thanks!

[TLSheff]

Recommended tranny services are every $50,000 miles so your slightly overdue for one. I would start there and see how she shifts after that.
Usually 1 filter and 7-8qts of Dex6