I have a two-faucet shower system, originally by Price Pfister. The shower has been dripping for some time. I replaced the stem and seat on the hot side, but that did not fix the problem. So, I did the same on the cold side. Followed instructions right down to the plumber's tape. What did I miss or is there something else I can do before I call a professional? Could I have over tightened something or not used enough brute strength? Thank you for your advice.

Did you remember to open or unscrew the stem before you tightened the bonnet nut?

I may not have done that, but which one is the bonnet nut? Thank you.

Just below the faucet handle you put a wrench on the bonnet nut, it's the nut your turn counterclockwise to remove the stem. Did you replace both the rubber seal and the brass seat?