My 2004 Tahoe is not running well and conked out on me the other day. I just had it repaired for some other reasons and the repair shop suggested we needed to have spark plugs replaced so it will run better. However, before then, it ran fine. I said no on the spark plugs, but now that I have it back it is running poor and I don't know how to describe it... It is glubbing, missing, on the verge of conking. The same thing happened to our minivan years ago and in that case, it was simply an air flow tube that was not pushed in all the way and once we pushed it in, all was well again.
The most common cause of this complex of symptoms is leaking intake manifold gaskets. Test for this by spraying a squirt of carburetor cleaner up and around the intake manifold. If the engine smooths out for a few seconds then there is a leak.
The second most common cause is failure of the mass air flow sensor (MAF). I offer no quick tests for this part short of swapping in a new one. Testing is done with graphing scan tool data and having an experience person interpret this data.
Other failures of possible, but this covers 90% of the problems of this type on this engine.