[Mitch//pa]

The FIRST thing I do for a miss is short each plug out to determine which cylinder is at fault, and at the same time you can see if that offending cylinder is getting a good spark."""" i then know where to attack"""""""...since you already checked compression etc try spraying or inducing propane around the offending intake runner on the cylinder not firing for an intake gasket leak. just another quick check or do the plug swap you already mentioned.
good luck i hope its something simple