My 1996 Merc. 60 is not maintaining power at high rpms. Last time out I took off in the morning and it ran like a champ the whole time until I got to where I wanted to fish, I mean scary fast! But after I was done (around 11:00am and it was hot! Like 100f) I fired it up and started out. It was running just as good when it suddenly hiccupped and started sputtering. From that point on if I went past half throttle it would begin to sputter and would almost die. I tried pumping the primer bulb on the fuel line but it was solid with pressure. Tried the choke to see if it helped but it made it want to die. Seems as though it is getting plenty of fuel. I replaced the plugs and started it up again but it had the same symptoms. Any one got any ideas on this one?