I would eliminate all the fuel, ignition, sensor, ECM related causes before I would pull the valve covers. Just my .02.

Depending on the year of your current motor at least the ones with Gen II cool fuel system often suffers from a bad low pressure fuel pump if not the inline fuel filter has been installed. The engine will still run even with the pump disconnected, but it will not rev out. No fault codes will show a faulty or clogged pump.
Check the fuel pressure at wot

Any updates?

He is correct. I personnally had a spark plug wire come loose on the plug (most likely not pushed on all the way). When you loose that cylinder everything works fine except you loose a % of the power and therefore max rpm's at WOT is reduced as well. In a car with full mufflers you could probably hear the difference when one cyluinder is dead but in a boat, especially with non muffled above water line exhaust I can hear no difference from in the boat.

Thanks everyone for your help! Sorry I have not got back with you on the update but I just figured it out today! Been working allot of hours and plus I have several muscle cars and the past couple of months have been consumed with going on the Hot Rod Power Tour. Too many toys not enough time. I have not had the boat in the water yet or even pulled it out of the shop this year. I changed my oil tonight and while poking around I did find a plug wire off of the plug. When this all went down I had a guy check all the wires while floating in the middle of the lake but should have done it myself. A local mechanic at Ugly Johns told me to change the water/fuel filter again, so I did. With a fresh oil and all holes alive now she sounded great in the drive way with the water muffs on. I will see how it runs this weekend, should be normal again! I hope so since I have been dying to get out on the water! Thanks again everyone, hope I can hang around more!

Shawn Tillotson
Split Decision Customs
Owasso, Ok.