always replace the filter when you change the pump. it's not normal for pumps to die that fast even if they are jobber pumps. make sure the electrical connectors& ground are clean& tight. also make sure none of the baffles inside the tank are broken and the tank isn't full of rust& dirt. i would empty the tank and pressure wash it then flush it out with lots of water to get all the crap out just make sure it's completely dry before putting it back in.