Help Please - 2007 Mercruiser 4.3L AlphaOne Engine Hesitation

Hi Guys I need some help please and thanks

I have a 2007 4.3L Alpha One Mercruiser Engine that is hesitating a bit on me. The motor runs fine at start up and idles at 800 rpm no problem. When I get the motor out on the lake it hesitates ~10% at mid and high throttle. When i'm driving it slows down 10% and eventually speeds back up 10% to the original 100%. The motor gives you the feeling that you have water in the gas but I have used only high test gasoline in the motor and I know that is not the case. I sprayed some Seafoam through the carb and ran the motor at 1800 rpm to see if i could clean out the top end but this did nothing to solve the hesitation and surge back up problem. I'm not sure where to diagnose next? Could it be I need a new fuel filter maybe, or maybe distributor cap, or new wires, ignition coil, fuel pump, spark plugs not sure where to look next? Any ideas would be much appreciated. Kind Regards.

Is it a tks

I don't think so. I have the push in choke button built into my throttle shifter. I used it once at the start of the season to get the boat going but from then on the boat does start with just the key.

Could it be I need a new fuel filter maybe,

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Ayuh,...... Examine the Contents of the filter, for any clues,.....

Last time you did tune up?

Hi Guys. I have confirmed it is a TKS turn key start. The last tune up has been a long time. When you mention tune up what does this specifically involve? And what piece could be a potential problem regarding my issue. Thanks kindly.

Update:
I changed the Fuel Filter/Water separator (with no improvement).
Took the boat out on the lake today and the max rpm was around 3700 trimmed. factory spec I believe is between 4600 and 4800. It has a 14" 20P prop with 4 blades (factory).

I have brought up new spark plugs, and a new ignition coil.
Its a 2007 StarCraft 18' with 4.3L mercruiser alpha one (TKS) carburetor. The engine compartment is very tight and changing the plugs looks almost impossible from above view. Do people take out the rear bench when changing plugs? Are there special tools, or mirrors required to see under the exhaust manifolds?

Any ideas appreciated. Seems way under powered right now...

Top speed was 54km/h on google maps. which also seemed slow.

I have brought up new spark plugs, and a new ignition coil.

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Ayuh,...... It ain't the coil,..... When ya change the spark plugs,. Do a compression, 'n leak-down test,......

That'll give ya a baseline, 'n tell ya the general health of the motor,......

The engine compartment is very tight and changing the plugs looks almost impossible from above view. Do people take out the rear bench when changing plugs? Are there special tools, or mirrors required to see under the exhaust manifolds?

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Workin' on boats,( 'n pretty much anything else)......
Ya remove whatever's in yer way of gettin' too, whatever it is ya gotta get too,.....
Bits of boat, or motor,.....
If a mirror helps,..... Go for it,.......
I once pulled 2 broken starter bolt bits outa a 3.0l tied to a dock, with a right-angle drill, 'n a mirror,.....
Sure beat pullin' the boat 30 miles to a shop, 'n pullin' the motor,.....

That motor does have the tks diode? an tks temp. sensor, that wires get mashed on top , from fuel line.