2008 Indmar 325 Assault surging

This past weekend my engine started having a surge at around 3000 rpm up to around 4K. Basically the rpm will drop a couple hundred at a time and catch right back up. Makes the boat feel like your riding a bucking horse. I’ve changed the inline fuel filter, spark plugs, distributor cap and rotational button but it is still happening. Any suggestions? Is it possible the water temp sensor or fuel pressure sensor can cause this. It’s just odd that it seems to run fine below 3k and above 4K.

2008 Moomba Outback V

Can you can borrow a fuel pressure gauge and run it?
If it's the fuel pump or possibly the regulator, that's an easy way to find out.

Next step, I'd check the throttle position sensor. Could be getting a dead spot on the contacts in that range.