It could also be the motor part of the pump itself. I went through several on the race car. They would be fine for about the first 10-15 minutes then quit completely. Half hour later they would run fine again. Went through 3 this way until we finally discovered a bad ground. We couldn't have the rebuilt because the motor itself burned out. Most of the rebuild kits I have seen only replace the pump mechanical parts.

You can test the motor with an ohm meter. On the Holley Blues and Reds it should read around 10-12 ohms. If it is a lot lower than that, the motor could be bad.