Originally Posted by TomKat
The trim thing is new to me so don't really know what I'm doing!
That motor doesn't sound like it's in limp home mode. It might be a touch under max revs, but that could be Trim/Prop/Load.
Trim and load are the free tests.
First off, I don't rate most phone GPS units. Mine often shows over 1kt at standstill - check this on yours.
Take the boat out empty and establish a base speed (take current/tide/wind into account by doing two directions and taking an average)
Then play with the trim on the motor. While under way in a straight line, at full throttle, trim out (raise the leg) in stages, listening for prop ventilation. You should hear the revs rising as you do this and I'd expect you to gain 3-5 knots. Eventually the prop will ventilate/slip and you need to drop it again to the sweet spot where you're getting max revs with no slippage. If you make tight turns in this trim, you will have instant ventilation and loss of thrust, so it's only useful for cruising/straight line racing.
The other thing I forgot to ask was have you checked the Lennie for water in the hull (is there a drain in the transom?)