1989 ford f150 6cyl stick MISS ON ONLY ONE CYLINDER

I just got a 1989 f150 4x4 6cyl stick.I replaced all plugs,cap,rotor ran seafoam 1/3 tank,1/3 oil,1/3 vacuum line booster.On the 2 spark plug to the rear of the 6 cyl you can pull the wire from the cap that is sparking but it doesnt make a difference on how it runs(the cylinder with the miss)I looked at the old plug that came out out of that cylinder and it was gapped at.055 instead of .044 and had hard oil sludge in between where the spark is on the plug.Any ideas so far on what to check? went through all vac lines.Thanks Born

I just got a 1989 f150 4x4 6cyl stick.I replaced all plugs,cap,rotor ran seafoam 1/3 tank,1/3 oil,1/3 vacuum line booster.On the 2 spark plug to the rear of the 6 cyl you can pull the wire from the cap that is sparking but it doesnt make a difference on how it runs(the cylinder with the miss)I looked at the old plug that came out out of that cylinder and it was gapped at.055 instead of .044 and had hard oil sludge in between where the spark is on the plug.Any ideas so far on what to check? went through all vac lines.Thanks Born
Check the compression on the cylinders then put oil in the cylinders and retest. If the compression comes up a lot the compression is bad. If unchanged pull the valve cover and look if the valves are working properly.