return pump not performing

[sirruckus]

head height is about 4' - although that wont matter when comparing the same condition to a weaker pump

I would expect some loss with the 3/4" line, but not 600 gph loss
I'll try changing the intake to a straight run.

the only other thing I can think of - is the motor is going - is there a way to inspect, or test?

I would think with the motor, it would either work - or not work