no pumps do not fail very often
but filters do get clogged up so i would replace them, even one in the tank.

check the drive cable adjustment and also the actuator on the drive pump linkage.
You also may want to get a pressure guage (5000 psi test guage) and connect it to the test port on the pump or control valve and see what pressures you are getting. The test ports are a quick disconnect fitting usually with a rubber cap on it. If i'm not mistaken the pressures for the drive circuit should be around 3000psi, i do not have a moffett manual so thats just a guess.
If you want to be certain on that get a manual.