Throttle or carb or both

[further]

Hey all, so was out on the lake today and it was finally calm. Boat starts easy and runs great, always has. Gets up to temp (about 140-150) and stays there. Cruised around for about an hour then was able to run WOT for a while and noticed that the rpm's would keep increasing as well as speed after a while... Longer than I would expect to take to get to WOT rpm's. In other words it seemed like there was more throttle being opened even though the throttle was all the way down. Hard to explain. I did trim up a little so that may have contributed and maybe this is normal, but I've also noticed that the rpm's drop off if I'm cruising and don't touch the throttle then I have to nudge the throttle a bit to get back up to where I was. Feels like the cable or something is slipping while cruising. So is the WOT taking a while to get to optimum rpm's and cruising throttle reducing related and possible due to the carb or is this a throttle issue? This is my first full summer with the boat and put maybe 10 hours since I bought it. Changed pretty much everything out except didn't do anything with the carb. They scare me lol
Any ideas? Thanks.