Along with the plugs at .030 and drilling the hole in the intercooler, look into replacing the lower coil boots. I am battling the exact same problem as you. Changed plugs at 60K or so after buying it with 50K on it, worked for a few thousand miles and then it returned. Recently drilled the hole and changed plugs again (I'm now at 70K) and it has not fixed it. Ordered the lower boots and just received them a few days ago. Planning on changing them this weekend.
Poke around on here a bit, you'll find a number of threads on this problem. Trying to read the sticky one that is 150+ pages (or more by now?) takes too damned long, though.