87 50 hp Mercury running very sluggish

Hey folks, I bought this boat last fall used it during duck season, fished alot this spring and it has ran like a top....a VERY fast top haha. But last weekend as i was running the St. Francis river it just bogged down after backing it off the trailer, I made a loop before picking up my nephew at the dock. i just ordered new plugs but I dont feel like this is the problem,I could be wrong because I am by no means a mechanic! It runs pretty normal when its starts up but it idles kinda rough but when I take off half throttle and full throttle are the same speeds. I am throwing alot of wake I but not going any where too fast....any help would be great thanks guys. oh yea its a 1654 Polarkraft 87 50 hp Mercury 2 stroke

Sounds like you may have dropped a cylinder.Look at your plugs & see if ones black or wet.

does your motor speed up but not the boat? If so you might have a spun hub on the prop.