Head gasket or EGR, & update on my head gasket repair.
Sounds like the head gasket to me - but it will be quick to determine if you take it into the shop. Is it still under warranty?
An update on my situation: Since I had the head gasket replaced, I have used my truck daily, and have towed our trailer (~8000 lbs) about 2000 miles, including up the grade (Hwy 299E in N Ca, from Redding to Burney, steep grade out of Montgomery creek) where I believe I blew the head gasket initially. But my last trip up that grade was in November 2006 - I will do the same grade again in a week (July 2007), in summer heat, so we'll see. But so far, in ~10,000 miles since the heat gasket replacement (including 2,000 towing), I have not lost a drop of coolant. There is no doubt that this was my problem, and the warranty repair seems to have corrected it. Note that I had the factory warranty repair - I would have opted for one of the after-market head gaskets and stud/nut combos if it was not covered under warranty, but the warranty repair seems to be good so far. Knock on wood.
Jim