I am having similar problems at surfing speeds with Stargazer. I've been dealing with PP and they are very helpful. I have a 2005 DBW MC. Here is the control test I performed yesterday:
1. In Control Test what RPM does it control at?
2. Does it hold very smoothly?
3. Does the “S” appear and stay on solid?
4. While in this mode, turn on your heater, bilge, lights, etc. The RPM should not jump up.
Scroll through your menu, under control settings, press the up arrow when you get to device test. Bring RPM's up to 1800 or so answer the questions. Turns out I have a bad ground, when I turn on the heater or tower lights, my RPM's jump. I hope the new ground will help my surfing speed problems. Otherwise I will play around with the other settings. I do know a KDW value of 160 is better than 120 for surfing. I will try 180 and see if that helps. Good luck.......