4 Stroke T50TLR over revving

[kodak guy]

Just recently while cruising above 3000 rpm the engine will rev up over 6000 rpm if I let it. I immediately throttle down to neutral and reverse the motor to de-weed the prop. It's a weedy lake, but not so much that this should happen as much as it is. I went to my backup prop, which has been sitting under the pontoon boat seat for 8+ years. After a run yesterday, with about 7 people on board, It still over revved too much for me. I'm going to make a mark on the nut, shaft and prop now to see if anything moves. I bought this boat and motor in 2007 and never had any problems with it until my grand daughter decided she need to be pulled behind the boat on a tube at full throttle, which for this boat is only about 15 mph with 5 people in it.
Thanks for the responses

[99yam40]

what is the RPM at WOT with a normal load?
are both props the same size and pitch?

yes verify if the hub is slipping,

is it possible that there is some cavitation taking place with WOT,
or turbulence letting air get to prop when at WOT?

[TownsendsFJR1300]

Sounds like a spun prop, especially with the extra load..