try checkin the grommets in the valve cover for the plug wires. if theyre not sealed right water/oil can get down in there where ur spark plugs are n cause it to bog a lil. myne did that too (especially on humid days). i pulled the valve cover off n the wires out. cleaned the wires n put the grommets back in with some silicone n was good to go after that. use some wd40 to get the water off the wires (if there is any) and get some brake clean to skwirt down into the holes there to get rid of any oil that mite b in there.....if this isnt the case then im stumped on this one....but it sounds like something to do with the ignition system.