SteffTX writes:

Is there a way to diagnose this problem.

You probably have a suction-side leak(s) somewhere in a joint. Can be
anywhere on the pump or strainer body, valves, or in the piping joints.

When I had a leaky PVC joint, I could dab on some of that blue PVC cement
while it was running, and the leak would go away briefly.

There are elastomeric gaskets beyond the O-ring in your pump/strainer that
can leak.