2008 DF 115 - RPM Fluctuation

This is a new Boat/Motor to me. Suzuki 2008 DF-115

Since purchase 2 months ago, the boat will start, idle, and run fine at low RPM's (just past idle). Does not stall at all. Once i get to about 2k RPM, the motor starts to hesitate. Or it's like the RPM's are jumping around like there's inconsistent fuel supply. The problem gets more exaggerated as you increase throttle. In fact, at full throttle, RPM's are just under 4K (barely getting the boat on plane) but will jump unexpectedly to 5500 or so when it seemingly gets enough fuel.

When the motor is warming up, it's the worst, but seems to get a little better as the day goes on. Also, at times I can find a "sweet spot" in the throttle where the RPM's seem to stay high.

So far I've changed the fuel filter, the Fuel Water separator, ran the motor from a 5 gal fuel tank that I know has good fresh gas, and checked for obvious wiring faults under the engine cowling. There are no kinks in the fuel line that I can see.

I feel like I'm headed for the repair shop, but is there something else I can check before I go that route?

Thoughts?

Thanks,
Bob

Spark plugs?

That's next. I'm planning to check that tomorrow. Anything else I should look at while i'm in there?

Fuel leaks water leaks,exhaust leaks,chaf wiring,oil level,all that stuff your suppose to do.

Vst chamber o-ring ?

It was the bottom spark plug. It looks as though it hadn't been changed in years and quite possibly never changed. It was VERY difficult to remove and we thought it might break coming out, but we got it. New plugs, properly gapped and she runs like a champ!

That bottom plug was slightly tucked behind the lower cover. Just needed to remove 3 bolts to be able to spread the lower cover enough to get a socket in there. I can't believe this would be the reason to not change this plug, but judging by a few other things not taken care of on this boat, I guess I'm not surprised.

Thanks to those who replied. I'm sure I'll have more questions in the future!
-Bob