[m5james]

What are you using to read codes? JB4 was giving me odd codes but Carista (an OBDII app) is what told me I was getting misfires and what prompted me to go two steps colder plugs with tighter gaps and hasn't come back since. I assume you've already done that though. As for a vacuum leak, it took almost a year before I figured out my leak was coming from the hard line between the engine and mufflers, which I deleted via removing one of the vacuum line T's on the passenger side in the engine bay which ran over to the fender and then ran the entire length of three car...easy 5 min check if you wanna try that. Fingers crossed you find out what it is since my meth kit is arriving today :-)