Over the past few months, I've noticed a dramatic drop in the water pressure in my shower. I changed the shower head thinking it was getting clogged. That didn't work. I still have good pressure throughout the rest of the house. The shower valve is a Temptrol, installed about 5-6 years ago. I tried the adjustment screw in the front but all that did was make the water mix hotter. Do I need to replace the entire valve?