Thanks for the tip. I found a plastic tube had fallen off that runs from the left side valve cover to the intake. Replaced it, but the truck is still getting worse. I'm thinking that I might have fouled one of the new plugs when it was running lean? The truck actually ran MUCH better right after I replaced the plugs a couple weeks ago. Now it's running rough again and so bad that it feels like it's on 7 cylinders.