Throttling up in neutral means nothing - forget about that tidbit of info - get it outta 'yer head.
Replacing injectors 'just because' is also a bad idea - forget that one, too - at least for the time being. Besides, they can be tested and rebuilt. Why would you replace something without knowing if it's bad?
As mentioned, start with pressure testing under load. Heck, you can start with it in neutral since if it's low then, it will definitely be low under load and no reason to take it out on the water. But first see if you've got the proper pressure getting to the injectors.
You need to figure out the general area that is causing problems - then you can start narrowing it down. Diagnose - don't just replace. If you're not comfortable with this, then hire a good mechanic. It may be worth a few hours of labor paid to a pro at this point so you can't get things figured out and start enjoying the boat.
Also make sure your cap/rotor/wires are good... and make sure the wires are going to the correct plugs.
Replacing injectors 'just because' is also a bad idea - forget that one, too - at least for the time being. Besides, they can be tested and rebuilt. Why would you replace something without knowing if it's bad?
As mentioned, start with pressure testing under load. Heck, you can start with it in neutral since if it's low then, it will definitely be low under load and no reason to take it out on the water. But first see if you've got the proper pressure getting to the injectors.
You need to figure out the general area that is causing problems - then you can start narrowing it down. Diagnose - don't just replace. If you're not comfortable with this, then hire a good mechanic. It may be worth a few hours of labor paid to a pro at this point so you can't get things figured out and start enjoying the boat.
Also make sure your cap/rotor/wires are good... and make sure the wires are going to the correct plugs.