Mike is THE number 1 Corvette sales guy in the nation. He has sold over 4000 Corvettes himself. Very knowledgeable and a straight shooter. You can pick it up from him, do a courtesy delivery at a local dealer or have it shipped to your house.
As I understand it you have about 500-600 hours on the injectors since they were last flow tested. I would recommend you do it again. If the problem persists then we can move to the next step.
Just to insert some real data, a 2000 Ford Excursion 4x4 with a 7.3 PSD is 7910 lbs no gear or passengers, but full fuel. I think a 97 F250 is a bit more than 5000 lbs. A 1995 Bronco with 5.8 is 5200 lbs. I have personally weighed both at a certified scale.
You will not get 80-100 hp by installing new rod bolts, Gil exhaust, fresh rings etc. If you are willing to get into the internals of the engine as stated, you might as well do it right. 80-100 hp will take a good heads and cam combo. Your existing EFI can handle all that with appropriately...
The problem with their test video is the Sharrow prop is basically equivalent to a 4-6 blade prop and they are comparing it to 3 blade units. It would have been more interesting to see a good four blade compared to the Sharrow instead of a 3 blade. The 3 blade props were weak in all the...
A small block powered 21' boat will get about 2.8 -3.0 mpg at cruising speed (2800-3200 rpm) on average. Higher rpm this will drop significantly.
Big block powered 21-24' boat will get about 2-2.5 mpg at the same rpm/speed (assuming normally aspirated!).
Drop 2 inches in pitch in the prop...
You can have your injectors cleaned and flow tested at many locations. Doesn't have to be marine specific. They just need the right equipment. They should label the injectors 1-8, flow test them before and afterwards showing the difference. They should be flow balanced too with comments on...
Referencing my spark arrestor comments, I mean the flame arrestor. The stock Merc one flows the best. Aftermarket ones perform quite poorly on these motors. Not that this has anything to do with your current RPM issue. It was simply a side-bar comment.
Good luck and let us know what you find.