I have a Price-Phister bath faucet that uses a ceramic cartridge. The hot side started to water hammer only when running so I replaced the cartridge. This fixed the problem and the faucet worked great. But a few days later, the water flow was suddenly very low as if there was little pressure in the line or a blockage. I flushed it out and determined the pressure is good. I replaced the cartridge just in case. Water flow is now only a drip! There are no leaks and pressure is good. Is it possible the problem is with the fixture itself? Cold side works fine. Otherwise I've screwed up a job somehow that I've done with no problem before.
I assume that since your PP faucet has a ceramic cartridge, it is of newer design, and probably has an anti-scald feature? Most of the Delta valves I have used utilize a ring that limits the amount of hot water that can be delivered. Is it possible that when you put it back together that the limiter is in the wrong position? Since you have determined that there is adequate pressure, I would assume it is either the valve or anti-scald.