i am unaware of any methods for testing.
if the cable is adjusted properly and not hanging up, and there are no visible signs of leakage from the lines, pump, blled screw, or tank, most likely the pump is bad.
has there been any work recently done to the sled? some if not all models had a check valve in the line from pump to the crankcase. perhaps the line was installed backwards?
over oiling could also be part of the equation in your loss of performance on top end.