I have a 2011 outdoorsman with the 5.7. I know it had a broken manifold bolt on the passenger side. I now have a tick on the drivers side and a misfire on cylinder 3 (p0303). It runs fine just cruising and under light acceleration. If I get over 3k on the tach it starts misfiring and throwing the code. I have religiously changed the plugs every 30,000 with oem ngk's from the dealer. Always run premium fuel 93 octane and always changed oil with 5w-20 Mobil 1 full synthetic. I just changed the plugs again and replaced the number 3 coil. Also did a compression test and have 195-210 on all cylinders. Still have the issue. Where could my problem be?

 

Maybe the fuel injector is fouled up. Try injector cleaner in the gas tank or pay someone to do the FI service

 

I have the same exact problem. Also changed coils and plugs. If you figure this out, please post it!