Well I plan on pulling the oil cooler soon and changing all the fluids. I'll check the plugs one might have fouled since it's been sitting for the winter.

 

Could also be an exhaust leak, that can make it sound like a mis-fire.

 

I suggest doing the PAIR mod.

makes it easier to diagnose problems...

 

This is my general opinion as well. Have you examined the entire exhaust including the headers and also the header gaskets? Even the studs, see the state of those. Kind of sounds like a good bit of air is getting out. I hear this same sound often when peoplle go into the shop with holes in along the pipe somewhere.