+1 What they said.
Here's what I did and what I learned:
1.) Rough idle/"shudder" -> regapped stock plugs to 0.035. The plugs weren't that far off to begin with, widest gap was 0.038/0.039, can't remember exactly, but they weren't 0.040 like some people found. Didn't help a whole lot.
2.) I put in NGK Iridiums, 1 step colder, gapped at 0.034, truck ran like SHHTTTT
worse mileage, poor acceleration. I don't think my EB needed colder plugs. Not only that, they had a weird white residue on all of them.
3.) Cleaned and Regapped stock plugs to 0.030, reinstall. Truck ran good again. No more rough idle. Shudder was still there at 55mph-ish in 6th like most of us had. MPG was back to normal.
My advice? Stick with the stocks, and gap them at 0.030.
On a side note... I've been experimenting with 93 octane. (I found a gas station here that has 93 for only $0.20 more than 87.) From what I can tell, the shudder is significantly less than it was previously with the 87 octane. I hope that helps.