happy hours

I recently repowered boat from stock 5.0 with stock 5.7 long block and it has a ton more bottom end torque ! it runs and planes significantly better. Boat currently has a 18" pitch 4 blade prop. Motor only has about 10 hours on it so haven't really wrung it out yet but seems to run great and very happy with it. When I throttle up from no wake zone speeds there seems to be a slight vibration around 2300 rpm and about 11-13 mph. If I leave throttle there it goes away like its a damped vibration or if I throttle up slower or even sorta faster it don't feel it or it goes thru the resonance so fast I can't detect it as well. Almost like it requires a certain throttle application to do it. It is right where the prop starts to bite and the boat used to sorta plow ( boat is stern heavy) -!: it jumping on plane and I have never experience cavaition so I dunno what exactly that feels lie. I can't seem to make it do it with steady throttle so do t think it's a missfire unless it gets masked and I can't detect it. While I was doing motor I also had local shop replace pinion oil seal and I did new u joints but prop has been same entire time. I have another prop I may try next time I take it out just to eliminate ate that from equation.