GM-GMC: Rough Idle, air intake hose, vacuum leaks

Question
I have a 2006 Chevy Express 2500 Van 4.8L. It has over 231000 miles on the engine. In the morning when I start it, it sounds like a surge of air struggling to flow through. The problem later in the day is it idles rough when warmed up, but am not seeing no service engine light. Prior to this happening. I had the lifters replaced, head gaskets replaced and other gaskets as well. I had spark plugs and wires replaced. The air intake hose was cleaned out, and I had the technician put it on a machine. They cannot find out what it is. Is it possible that there is a vacuum leak? If so, what parts or components greatly effect vacuum leaks. I hope I gave you enough info. Thanks, Jim.

Answer
I suppose it is possible that it has a vacuum leak and depending on where the leak is it would cause different concern.  However that will generally result in a fault code being set due to lean exhaust or something like that.  As for causes of rough idle.  With that kind of mileage it could be many things.  A partially clogged injector, a weak coil, a partially burnt valve.  What I would do is install a scanner and display the misfire data.  If there are cylinders that are misfiring it will display which one or ones and you can begin to narrow your search there.
Hope this helps a little.  If you have any fault codes I may be able to help further.