I have a triple handle system in which I have recently changed the hot and cold water stems and the diverter stem. The manufacturer is Price Pfister for those of you who are interested. From the second I have replace the stems nothing seems to work correctly. First, when I turn on the diverter for a shower, half of the water continues to come out of the spout. Secondly, the now half powered shower runs out of hot water while my sink and every other faucet in the house continues to have hot water.

Sounds like the seat in the diverter has some crud blocking it so the washer can't seat Remove the diverter stem and washer and turn the water on to flush it out. Since you have crud in the diverter seat perhaps you have some in the hot water supply that's moving up and blocking that seat also. Shut the water off, remove the hot water stem and flush that line out also. Put everything back and try it now. Good luck, Tom