88 Larson merc 350 will not rev past 3,000

My 88 Larson will not get on plane. It only revs to 3,000 rpms.
Things I have done/replaced recently:
New spark plugs gapped to .04 NGKs
new cap/rotor/spark plug wires
chevy 350 fuel pump (had laying around/changing over winter to marine)
new fuel tank check ball fitting
bypassed water-fuel filter

Has a slight miss at idle
Shuts off frequently at low speeds when parking/goes in neutral
Rpm guage sometimes moves to incorrect rpm/fluctuates then returns to normal

Does not backfire or sputter when I hammer the throttle down and hold it
does not backfire/sputter period
It bogs ever so slightly when you first try to take off.
Revs fine without a load.

Going to re-time it soon-messed with distributor and don't have a light at the moment. I really don't know what else it could be. Thanks for all the help.

would help to know what the motor`s hooked up to.

Bt Doctur said:

would help to know what the motor`s hooked up to.

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I Think that it has the thunderbolt iv system.

Great news but that dosent tell us what its hooked up to.

It's got an alpha outdrive if that's what you mean.

Thats better. some causes are:
damaged or incorrect propeller or incorredct outdrive gearing
incorrect firing order. dead plug wires, dead plugs
compression test, cylinder leakdown test would be next