Prior to the water not shutting off the water pressure was better, but still not good like it should be. Like I said, it was great when I first bought the place 4 years ago, but has gotten worse in the past few months. After the hot water wouldn't shut off about two mornings ago, and I had to pull the stem to find the screw and rubber washer laying inside, which is why it wouldn't shut off. All that was left of the washer was about the size of the screw head, but was swollen, so the outer portion of the washer is missing. I installed a new washer and that fixed the problem with the shut off. After the repair is when the pressure became almost non-existent. This is why I'm thinking the missing portion of the washer could possibly be what is clogging the center of the diverter.
I know the fixtures are something common that starts with a P, can't remember what they said it was at Home Depot...Puritan or something. The guy said that they were very common though.
I have access to the back where the pipes are through a cut out in the next room. I guess I'm planning on investigating the attic first to see if I might have a pinched or kinked vinyl tubing or something. At that point if I don't find anything obvious, I guess I will desolder the diverter, attach a piece of tubing to run to the tub, and turn water on to check pressure. If I have good pressure, I guess I'll be replacing the diverter if I can't get it cleaned out.
Does it sound like I'm on track? Believe me removing and replacing that diverter is the last thing I want to have to do. Been a few years since I've soldered copper, but I was pretty fair at it. Just kinda a tight space to be working. If you have any other ideas I am open to try anything before that.