My 2007 Outback with Indmar 325hp is bogging down especially when loaded down and hot. 225 hours - excellent shape and well maintained.

This is a new issue which started this summer when wake surfing. Happened when loaded down with 1000 lbs of ballast and people on the boat. Ran fine for a while but when heated up - after an hour or so - would bog down bad and idle rough. When the engine cooled off would run much better - but still bog down in odd ways - for instance at 3000 rpms the engine would just start to bog down by itself to 2000 rpms or so and then run back to 3000

I changed the plugs, fuel filter and Distributor. Everything worked great for about 20 hours. Now doing the same thing again. Something is wrong - not sure where to start?

Worried we are pushing this boat to do more then it can? Appreciate any advise.