pp keeps dropping speed

hope some can help me
I put the Perfect Pass cruise in the other day and took the boat out for a spin .I had the light on the controller blinking and when I reached the right speed pressed the engage button. The light then turned solid red and I thought sweet .But ; and there always is ; The speed would stay ok for about 10/15 secs then it would drop off.I can't actually remember the engine changing pitch either to compensate for the extra load of the rider .
My wife has had a clean out in the garage and threw out the box along with the instructions after I fitted it .Can anyone help me with this .
The coupling thingy that goes on the end of the throttle cable had no gap at in stall as per instructions .What next .

Go to their web site... you can get the manual online. And frankly, it's right on in terms of trouble shooting... follow it to the letter. (For example, pull a little slack cable out of the servo and then turn on the motor. The servo should "auto tension" and pull in the slack)

Or phone PP. They are very good at trouble shooting. I'm will to be it's a fairly minor thing.