boat stalls out at 2000 rpm

I have a 2005 stratos 21 ft with a mercury 250 3.0 efi motor. the motor runs good but lately when I hammer it out of the hole it will go to 2000 rpm right away then it just stays there. it will slowly climb out of it and when it hits 3000 the engine takes off and planes out. once on plane it will run 70 mph and like a Cadillac. the engine doesn't cut out or die. just sticks at 2000 rpm sometimes for half a mile or so. don't know if a fuel issue or what. already replaced all the plugs. any help will be appreciated. and a side note, there is a 21 ft stratos for sale.

Ayuh,..... Sounds like a fuel delivery issue to me,.....

Suggest you post your question on the Mercury Forum.

Go to top left of this page, click on "Forum Home", scroll down outboards to Mercury, and post there. You're likely to get more help there.