That's exactly what it is, Jorge. The 17-M series props are the early Yamaha salt-water props, and provide as much stern lift at high RPMs as the Mercury Mirage. Their weakness is in a reduced rake progression on the outer 1/3 of the blade, which gives them great top-end performance, but weakening their mid-range performance. They run very well as a semi-surfacing prop for WOT/high-rpm performance, with slip ratios that can be down around 8%, but have higher 15%+ slip ratios at greater running depths, at mid-range RPMs.

So I guess I need to be running WOT all the time

Naw It's just the prop that came with the motor.
As the budget get better I will look for a "all around" prop
Most of the time you run in the mid range anyways

I know that you have extensive knowlege on props what do you suggest??

Jorge, I think the best easily available all-around prop is used is the Quicksilver Mirage. I would also suggest either the 17" Pitch, or 18" Pitch, assuming you have the 1.85:1 gear ratio lower unit. If you have the 1.65 gear ratio (which would be unusual), then the 15" or 16" pitch is in order.