Thanks for the input guys I’m changing the other three Spark plugs now,
Just bought it about a month ago , i drove it home from Vancouver BC to Prince Rupert BC just below Alaska (about a 16 hour trek) and all seemed to be fine, opened it up a Couple times In 5th gear but wasn’t honkin on the motor by any means as I’m new to Subbys. The CEL came on about half way home (where the symptoms started) so I took it easy on her the rest of the way. When I got home I plugged in my code reader and I got a misfire on cylinder 2 so I changed the spark plug on it aswell as an oil change (a litre and a half if that of the blackest oil I’ve ever seen came out of the poor thing) fired it up and seemed too be all Gravey. Had no CEL and sounded A lot better then it did so I took it to the highway tryed again and still a studder/power loss with it in 2nd and going about 85% on it. No CEL this time.Thought maybe fuel filter at first but again I’m new to these machines.