I've installed two new shower price pfister stems and seats for my two handle shower faucet. The problem that I'm having is that I can turn the handle a 1/2 turn before the water starts flowing. The opposite is true when I'm closing the tap. I feels as if they are over tightening. I've tried to change the handle fixture, but I still have the same problem. In my other showers, the handle reaches the closed position and go no further (I cannot keep turning the handle and over tighten)

Have you tried loosening the bonnet packing nut? That's the nut on the stem. Let me know if it helps. Good luck, Tom

I tried that and have at as loose as possible without it leaking from the stem. Still the same problem. Any other things I can look at?

You might try lubricating the threads on the stem with Silicon Jel. You are quite sure that you have the correct stems aren't you? Something's binding in there. Lubrication might just be the answer. Good luck and let me know. Tom