Hi, my name's Mike, I've been a longtime browser of this website, but first time posting. I am hoping someone has some ideas to help me...I have a 2005 60hp Merc bigfoot EFI on my pontoon boat, and I have been experiencing some power loss which is progressively getting worse. The issue occurs ONLY at around one third throttle or higher where the boat will suddenly lose power after running fine for a short time, as if the throttle is being pulled back. I have to then pull the throttle back to idle speed or it will stall. If I wait a few seconds I can throttle back up and continue on. Also, if I keep the speed low the motor runs just fine. This began last season, only happened once or twice, now this season it has gotten worse to where it happens all the time. I have replaced both fuel filters, and there is no change. I also changed the thermostat after I got a temperature warning once, but I'm not sure these 2 things are related, no heat warnings since. Thank you to anyone who can point me to what I should look at next.