I however had the advantage of knowing that it was definately not a prop issue.engine runs great, rev to 6K in neutral, no backfiring, missing, smoke, very smooth running, just can't get over 2200 rpm cruising
If you have the in-line canister fuel filter before the carb, this is a possibility. A couple of weeks after changing out mine with a new one, it failed. There was what seemed to be a blob of caulk inside. Must have been a manufacturing thing since there is a primary Racor filter upstream.
The second time was an ignition issue the following season. About a month after doing a tune-up, I replaced what seemed to be a perfectly good (new) cap and rotor and what was a new plug wire, and away she went.
Bear in mind that in both cases, the engine seemed to sound and run perfect, and in neutral under no load, would rev up as you described. Under load however, everything changes.
A few simple tests might save you some money.