Sounds like 52degrees has got this one down. California smog tech? Are you an L1, too? I am, only 1 of 2 in this county (what can I say, we don't have any emissions testing here yet, let alone IM240).
That's where I would start, too. The condition will get progressively worse, as the plugs get more fouled. Replace them after you've fixed the root of the problem. A sticking EGR would cause a rough idle, but would also cause your brake pedal to be hard because of lack of vacuum. However, your truck is OBDII, check codes first, and go from there. The diagnostics on that truck are very good, guessing is just pissing in the wind. A leaking regulator would set two codes, rich condition bank one, and rich condition bank two. I know the lean codes for this are P0171 and P0174, don't remember what the numbers are for rich, but is may be P0172 and P0175.