2000 Century rough shift to 3rd and overdrive

[Locust Hill]

I previously had rough shifting throughout and had the pressure control valve replaced. Then less rough, but still noticeable shifting began in going into third and then to overdrive. This goes away after some driving and things have "heated" up. Any ideas

Still have this problem. Dealer says it's dirt on the plates and beyond what they can get to with a wash. Says it will go away with some driving, and it does. Is it the dirt, and is the dirt getting in solution with the fluid, thus cleaning the plates. If this is the case, why cannot one drive the car till the problem goes away and then drain the fluid out with the dirt and refil with clean?

[Gokartz01]

I dont know but all I have to say is tranny fluid..