first. why would it have a 1.36 drive? I cant imagine any one setting it up with a 454 mag and a 1.36 drive as it would be a dog. second, 69 mph at 5700 is around 25% slip with a 1.36 and around 16% with a 1.5 ratio which seems more likely.
the part I dont understand is if the boat ran good with the original setup and all that changed was the increase in horsepower then it should run the same now but pull more rpm. the boat handling as far as getting on plane and any speed up to the original mid 50's should not change. the only reason it would blow out now getting on plane is if the motor makes no bottom end power and has to cavitate the prop to get the power up. that should not be an issue with 500 odd horsepower.

as said above - If the only thing that has changed is HP then It wouldn't change getting on plane. Should blow out the same with either engine.
More HP will just mean more RPM and speed. The engines weigh the same so no change in CG. Unless you changed from stock exhaust to tubular headers.
And for top speed the tips of the propeller blades MUST break the surface to free up the prop. How far below the hull is the center of your prop shaft when the prop shaft is parallel to the bottom of the boat?

Did you add a drive shower when you upped the HP and then started having this problem ?

Ok guys prop drive is 1.5 for sure just pulled it, i dont know why all the slip getti g on plane i assumed because of more hp and torque, center of prop shaft to bottom of boat is 8.5 inches, i did not add a drive shower still running same one as last motor and same drive, the previous motor never blew the prop off never cavitated, but this thing is bad , happy ish with speed when i get it there but went on poker run added 2 guys took me 4 times to get on plane it cavited so bad on take off if you dont baby it to the extreme it will cavitate so bad you have to set her down and start over

Same exhaust as well

And i agree no weight change, and i appreciate your guys feed back on my issue, just got done pullin drive and carb after winterizing.

Compedgemarine if i could get traction this thing would be a missle getting on plane, i dont understand why iam slipping so bad

Coupler bad, slipping getting on plane?

Curious to see what is gonna fix your problem!

I orignaly thought that but thats not the case, it just blows prop free , complete lose of traction when u add any type of power