Seafoam Trans-Tune fixed my harsh shift!!
I had the problem that folks diagnose as a PCS solenoid problem. Harsh shift from 2-3 and 3-4. I paid 10 bucks for a can of Seafoam Trans Tune, poured it in, drove home from the parts store (about 10 miles) and the next day the transmission worked perfectly. I couldn't believe it so I've driven it all over town this weekend and it has been perfect ever since I poured the stuff in on Friday night.
I had to let everyone know.