I still have somewhat of a mis-fire phenomenon occuring at idle speeds that disappears above 1500 rpm. Having already replaced every ignition component on the car and gone through the entire fuel system, I'm inclined to think it's a mechanical problem.

The engine has passed compression and leak down tests and there is no blue smoke coming out of the exhaust, so I'm also inclined to believe the bottom end is ok as well as the valveseats and valves.

The only other thing I can think of that would cause something like this would be a faulty lifter

Any thoughts?

 

No

vacuum leak

 

Doubt it. You'd have a nasty valve tap if the lifter was collapsing.