I have an outside set of outlets all hooked up with GFI's. The last on the run is used for the small pond pump. It runs for about 3 days then throws the circuit breaker. If I hook the pond pump to my front yard outlet, it works forever. I didn't reset the last GFI and ran the pump off my second outdoor GFI and it tripped the circuit breaker in the house. I'm now running the pump on my third external GFI. I run all sorts of power equipment off the second GFI and it never throws the breaker or the GFI. Could I have a faulty circuit breaker. Should the GFI throw before the circuit breraker-- it kind of defeats the purpose of the GFI, if the breaker goes first.

A GFI and breaker trip for very different reasons. A GFI is NOT a circuit breaker.

The breaker never trips when using all sorts of equipment, but it trips using the pump, yet you think the breaker is bad? Then why isn't it tripping while using the other equipment?
Sounds to me like the breaker is doing it's job and you have a bad pump.

Or, it could be that the circuit where it is tripping has other loads and the pump is overloading it, where the one where it runs forever has no other loads.