brick

Pick whatever brand headunit it you like. Not sure from your description if the amp is running all the 6.5 inch speakers or just the sub. A separate amp running the 6.5’s will give much better sound than running off the head unit. Run the 6.5’s on “high pass” to remove low bass frequencies. Adjust crossovers to taste.

Buy the parts while you can still get them!

Did you replace the IAC muffler when you replaced the IAC? brick

I like to prop for the upper-end of the recommended WOT RPM range. Your boat is at the bottom end of the range, so dropping to an F4 propset would help. Hole-shot will improve, boat will hold plane a a lower speed. Top speed will not change much, but your RPM’s will be higher for a given speed. Dual prop drives do not need ( or like) much positive trim.

To me it sounds like a fuel issue.

Are you having any starting issues? A bad IAC or missing IAC muffler will sometimes cause a hesitation from idle.

Find a junk boat

The 220SSi is a wide, heavy boat. The best thing you can do to improve performance is remove weight. Get rid of anything not needed or safety related. Run with less fuel. The bimini really slows you down. I pick up 4 mph with the bimini and tower board racks/ mirror removed. But most of the time we are just cruising at 3000 RPM/30 mph.

What speed (GPS) and RPM are you seeing at WOT? the 220SSi is typically a 50 mph boat (top speed) and likes to cruise around 30 mph (3000 to 3500 RPM). A 19 inch pitch prop (single prop drive) is typical.

You won’t the lottery!

I have had a few blue plugs break over the last 16 years on my 2005 220SSi with a Merc 350MAG/MPI. I keep spares. I suspect over-tightening is the culprit.

When was the impeller replaced?

Someone will need them one day! Don’t turf it! brick

Sealed gimbal bearing on my Merc B3

Chaparral only keeps skins going back about 5 years.