did you rebuild it yourself and how often do you do oil changes? i rebuilt a cvh a couple a years ago and through testing it 15k after a rebuild i made it rev to 7.5k. it coughed a bit and it was sluggish after. i stripped the engine down and found that some of the white metal bearing liner material had come off and found its way into the engine, oil pump and oil galleries and was causing a small blockage. also found the oil pump had scores in the rotor, this would cause low pressure too.