I have a 2000' mercury 225 EFI. Here is what it's doing. It will start and idle just fine , rev up as high as I want it to go in neutral. Once I put it in gear , it struggles to plain off like it's starving for fuel. Once it does get up , about a minute later , it has very low power under 3000 rpm and once I take it over 3000 rpm it dies and just a few seconds later it will start back up , back under 3000 rpm . I have recently rebuilt the fuel pump , replaced the fuel filter and the spark plugs. I am lost as to what is going on. And the fuel pump was the " gravity fed " fuel pump. Not the electric fuel pump. I'm sorry if I don't know the correct term guys.

First thought I had was to check your lower unit.
Then I re-read your post.

How old is your fuel line? Do you have a water separator on it?
Primer bulb age?

How about checking fire on each cylinder?

What did the old plugs look like when you removed them? Any wet ones?

Ser. number? Sounds like a throttle position control problem, electric fuel pump screen in the VST. These motors the TPS is very sensitive.

Fuel line is less that 2 years old. Yes it has a separator on it. Each cylinder does fire. When I replaced the plugs , all seemed to be burned normally. All 6 looked the same. No wet ones. I always run stabil with every fill up as well. I think I'm leaning toward an electrical issue from what Gary Purdy says.

where you located I have shop in McKinney and could look at it for you

I live in Weatherford. I actually committed to a guy that has a shop in Alvarado. Since I already committed to him , that's where I will take it. But in the future I will keep you in mind.

Thanks!

sounds like a bad fuel line from the tank to the motor.

power packs/coils? maybe?