Perfect Pass Help

My PP runs fine in RPM mode. However, I took my GPS along with me one day and discovered the PP speed was off by about 3 mph. I decided to switch over to the speed mode (vs RPM) and I calibrated the PP to the GPS. Got it dialed in and tested it a couple of times. PP kicked in and held speed perfect. The next day I go out and set the PP (21 MPH) in speed mode. I get the boat to speed, the PP beeps, I turn loose of the throttle, and immediately to boat looses speed as if I had pulled the throttle back. This happened 3 times in a row. I switch back to RPM mode and everything appears to be fine. I inspected the paddle wheel and it turns freely. The only thing is that the arrow on the paddle wheel points slightly toward the side of the boat instead of directly to the bow. Anyone have this problems or can offer any advice. I have checked with PP and they appear to be at a lose. Thanks.