Moen has two similar models. One is pressure balanced, the other is temperature compensated. Both are easily serviced, most times you can get parts at box store. I discovered that once in a while I was able to create a problem by leaving the shower valve open (on) and then cranking the water supply to full on. The inrush can sometimes hammer the balancing mechanism into submission and simply taking apart and "unjamming" things can fix that problem.
2002 Monaco Diplomat 36PBD, Avalanche toad, Glastron MX175 , X5 BMW, Almost enough toys, 3 dogs. 1 longtime wife(48 yrs)