Finally took her out yesterday by myself and the day before with 4 people. Same problem 7-8 mph at not more than 2200 rpm throttle all the way down. Did not try chocking it while underway. Will try again. I'm leaning towards fuel pump and carbs, because we have compression and spark on all cylinders and we have fuel.

Just like most of you said, it was a fuel issue. Although I can't tell whether it was the fuel pump or the carbs because it worked on both. New fuel pump kit and removed, cleaned and did the gasket kit and all three carbs. She's running smooth with an 800 rpm idle in the water.
Once again, thanks for your help! :sun: :beer:

great news, i hate it when i do two things and it works and then i don't know which one was the fix. but it is better than when i do 2 and none is the fix.