Thanks Flatrater for the pics. Like they say, they're worth 1000 words. So it looks like the groove that's worn in the solenoid's armature causes it to hang up in the low current/high line pressure state which causes the jerky shifting. On my car this seems to happen only when the car is thoroughly warmed up and will remain until it cools off.
You describes somewhere that the PCS can be changed without removing the transmission and only lowering the cradle. I'm almost ready to try this myself on my 2000 Century. If I remember the time I changed a FWD transmission on a GM, you'd only have to disconenct the steering, the struts, and a couple of engine mounts. How about engine hoses/cabling? That may be possible with what I have to work with (basically, a floor jack and standard mechanic's tools). Does removing the side cover require draining the fluid first? Is the PCS exposed once the side cover is off? Any other pitfalls? Once I start, I won't be able to move it easily.
One more thing, I had a couple of instances of my TCC malfunctioning I think the code was P0742 TCC System Stuck On. That caused really rough shifting. This seemed to clear itself both times, but happened on a road trip in both cases. Could the PCS problem have anything to do with the TCC? Any advice is welcome.