Pumps require more power as the flow increases.
You have a problem that is common when submersibles are selected for irrigation service where the head requirements may be low. You can get too much flow through the pump. I believe the pump you have is rated at 24 GPM maximum.
Is the pump actually installed in a deep well? Sometimes people put pumps selected for a deep well in a lake and the motor is overloaded. The usual pump sellers will sell well pumps for everything. You usually want a pump with fewer stages if you are not going to run it at high head.
The Franklin manual
http://www.franklin-electric.com/Manual/pdf/fullAIM.pdf (page 16) gives maximum service factor load for 1.5 HP 3-wire pump as Yellow 11.5, Black 11.0, and Red 1.3 Amps. That matches your observations.
Check the current at maximum recommended flow for the pump.
Your tank is very small for that application. You have a situation where a Cycle Stop Valve and/or some kind of flow limit may be the best solution.