well, I talked to reeflo today. He thinks it is due to the valving back, even though it sounds as though other people have throttled back this much successfully. Anybody want a new barracuda pump???

id put my money on the type of inlet reducing the flow too much making the pump work harder then it should.
also since its an external pump would it really affect your water temp?
the actully pumping part is separated from the motor.

my dart told me not to reduce the inlet pipe size and to keep the line strait without any bends.

For high head pressure applications like your sump's return you would probably be served better by a high pressure pump rather than a high flow pump anyways. The Panworld are said to be less expensive version of the Iwaki which are a top of the line Japanese pump.