21% slip at 106. If it was just a matter of slip I would just run larger pitch props and let it slip. I don't care for them breaking loose before they should.

Have you checked the hull for straightness, hook???, sharp trailing edges???
If you get on plane OK with the props you have but blow out at top speed - sounds like something else might be wrong.
Drive toe in or out depending on prop rotation?
Wrong style props?

How high are you trimming it at top speed. Do you have a cable indicator? What # is neutral, What # for top speed?

Can't really use the trim at all and it does not blow out on flat water. Glass smooth water and running over a boat wake will sometimes get them to break loose. It's hard to describe but I can't tell they are right on the edge of traction. That's why I feel like I'm close and going to try the other props before the spacers. Also the props I have been trying don't have much cup out by the tip and I know that can cause some of this.

What are you running to slip at 21%, 4 blade props with shorty drives, that's embarrassing for a 42 lightning, if so, space down, pitch down, and blade up.

did you read any of the thread? He has Ssm 4's on it. No shorties for those. And 21% is only about 5-6% off what I would expect for that boat.

With my heavy ass cig my slip is 11%.
They are too far out of the water, I bet the rooster is impressive. I`ve tried about a dozen props, and 2" spacers and switched between in/out a couple times over a 4 year period. That would be my advice.

17" of diameter should be fine for this hull. Putting the propellers 1" deeper in the water should only help, not hurt anything.
Additionally, having the propeller gone through and face lifted could help greatly.
Also, depending on what is in the cabin, your CG may be slightly forward.

Let us know if we can help with your propellers. I'd love the ability to discuss this wit you.

Brett

Brett gave you another option here, drive down, diameter up, pitch down.

What motors are in the boat???