Had low hot water pressure, especially in upstairs bathroom sink and shower/tub. Draining heater didn't help so I replaced water heater. Great hot water pressure in bathroom sink but no improvement in tub/shower. Very perplexing! Replaced valve and springs/seals. I can't figure this one out. I have to be missing something but don't know what. I'm hard pressed to believe that the 1/2" line is obstructed, but......As stated, the improvement in the sink was dramatic and they're what, 4 ft apart???? Thanks in advance for and insights and/or corrective ideas.