Did you do anything to change the cavitation plate above the prop. It is there for a reason. Small changes to the cavitation plate can cause huge changes getting on plane.

something is not right or everything is perfect and he doesn't realize it.
He went from a 454 at what 360 HP ( guess ) to a 502 at estimated 550 HP and gained 11 MPH.
Sounds about right to me.
Going from 58 to 69 MPH the boat is going to feel a lot looser.
It can't be running bow down or he wouldn't be doing 69 MPH.
I still want to see that picture.

It is possible for the vent holes to suck air through the exhaust passage through the drive. And it seems to blow out just as stern, transom assy, and top of drive come out of the water. Plug exhaust hole at the top of the drive. You can also epoxy up vent holes in the prop. Also, is the prop spacer correct? A long spacer causing prop not to be sunk into the ring on back of the bullet will make a big vent ring all the way around the prop.

try without tabs seen lots k planes or tabs that plow try trim in as in down negative trim check on lift or trailer

Water in the bow???Jack the front up as high as you can with the aft drain plugs out I have my trailer jack up on three blocks and fully extended so I could get all the water out of mine.

And with water weighing approx 7.5 pounds a gallon it wouldn't take much to give you your symptoms.

Did you add the tabs during the repower or were they part of the original setup. Something other than power must have changed. We had a 230 that went from the 330hp 454 to a 450hp 502 and we had good results with 23p Mirage prop. You might try a 25p Mirage to get the rpms down a little but I doubt much speed is left. That boat is built like a brick (4600+) so your doing good hitting 69.

My money is on the drive shower causing it. Maybe when it was reinstalled it hangs down further than before. I've seen it numerous times. Something is definitely disrupting the water flow. It's not the prop causing it I'd remove the drive shower and try it. Post a photo of the back of the boat, maybe someone will notice something. Did you add a transom water pickup by chance? I've also seen those cause similar problems.

^^^Thanks. :)

Yes way.
​​​​​​​I have been a live witness to this, and many other people between the boating sites.

I just read the 1st and last page, Did anyone bring up your Trim Ram Pins are in the Rear position? so the drive will come further in?

The drive shower was there with the 454.
I think the drive is not going down all of the way.