Merc 7.5 "slipping"

[stealurface]

Can someone give me advice on what the problem may be.<br /><br />MErc 7.5 - when on the lake - I try to go WOT - it won't get there, then after about 3 minutes it kicks in and pushes, then kicks back out. Happens about 3 times, then it goes full WOT no problem.<br /><br />Carb? Gears? Where should I start? Did full decarband changed oil in lower unit already. <br /><br />Thanks in advance