Good afternoon! I have a early 90's 8HP Mercury Mariner. Overall the engine runs really good, however I have noticed when I run anywhere from 75%-100% throttle, it begins to slip. I can hear the engine grow louder, but it begins to slow down. I typically slow down when it starts to do it and putt my way in. It also happens periodically. Could it be my prop? I appreciate any advice or suggestions.