Mine was doing the same thing. I have a 98 Merc 90hp, it has a 4 blade prop on it and I thought that could have been the problem, but before I started to make big dollar repairs or replace the prop, I did a couple of cheaper things, First I changed the fuel filter, it cost lees than 20 and then changed the plugs, replacing them with NGK's and also went to a higher octine fuel and also started usung Merc oil in the fuel.My boat does not bog down any more and comes up quick and runs great. Check these simple things out first and it could save you a lot.