Carol, I’m not exactly sure what your question is, but it amazes me that you’ve gone through five water pumps! Has anyone been able to determine exactly what is causing the pumps to fail? And more importantly, which component(s) on the pump(s) are failing?
ShurFlo has a very fine product line and stands behind their pumps. Personally, I’m a big fan of their pumps. Here's a short video highlighting the features of one of their newest pumps.
Also, keep in mind, it’s difficult to simply wear out an RV pump, especially with the unique design of the ShurFlo pump head. Be sure you have a filter/strainer installed between the tank and the pump. A regularly cleaned strainer will keep particles of what I call “tank trash” from migrating from the tank to the pump, causing harm. And be sure there is plenty of ventilation around the pump motor. If the motor is component that is failing, it could be heat related, but they are equipped with an integral, automatically resettable overload protective device. I would love to learn the cause of those failures; as would ShurFlo!