First post on this forum...so right to the question. I have a 2006 F150 with 125,000 miles on it and have never had or did a tune up on it. I have a Superchip in it along with a cat back and K&N cold air intake. This truck has been a screamer! I change the oil every 5k with full synthetic and do the trans fluid change every 25k. Never a issue with this truck until last week. Started to get the dreaded chug alug when the OD kicked in at around 42-45 mph. I instantly took it out of OD and it ran/runs fine. That is till I partial throttle it and then I hear and feel the miss. If I WOT it, it gets half way through its powerband before really missing/sputtering at which point the check engine light starts flashing. I have to do this a few times in order to get the CEL to stay on at which point I plug my Superchip module in and it tells me there is a misfire on cylinder whatever one it is. I proceed to change that plug and then test drive it with no issues.....until a day or so later it starts doing it again of which I find now its a different cylinder. I have now changed out all but one plug (can you guess which one it is?? LOL) and it seems to be running fine today. But what gives? Why this one then that one then that one on that bank etc... Is the computer sensitive between the old and new plugs? And no I haven't sprayed water in the engine compartment nor does it rain here in sunny southern Calif. Any ideas?