Try a new lifter in the #5 valve[s] that have the adjustment issue. I have had this issue too on old tired sixes and SOMETIMES this fix works. If the engine is that tired, it doesn't even have to be a new lifter, just a known good lifter that is still convex or flat (but not concave) will do. Even the difference between 105psi 120psi can indicate this problem.
Could also be a cracked valve spring - similar subtle change in compression check and it will "seem" to hit all 6 off idle.
Could also be a vacuum leak, but then it seems #6 would also skip now and then.
Also try swapping plugs and plug wires and see if the miss moves cylinders.
