Dead Cylinder Below About 1500 rpm's

Not to be an ***, but why are you here, arguing with people trying to help you? You could have whipped that valve cover off ten times by now and confirmed or denied a broken valve spring. That would really narrow it down, too. BAM the valve cover is off. It's that simple.

Lastly, you should listen more. Roy and Charlie have close to 150 years experience between them. I have also seen a slant skip on #6 because the power brake hose had a hole in it. The skip only showed up at idle.