Just to confirm, the engine acts the same both cold after sitting overnight as well as hot? As well, the ONLY code that you have is a random misfire. If that is the case, the sensors may not be your problem. (Sensors and coils tend to show symptoms, before they completely fail, when they heat up.) If both hot and cold problem and no other codes, I would look more for a mechanical problem like a leaking vacuum hose or bad spark plugs that were not gapped properly or the wrong ones that have carbonized over.
Since the head gasket was replaced a month ago, were the spark plug wires replaced at that time? If not, there is a good chance they are bad. Often removing wires on the 3.4, if on for a few years, the wires can almost weld onto the spark plugs, resulting in the wires being stretched and destroyed at the end connectors. Same for the plugs, they should have been renewed too with the CORRECT ones. Finally, if the head gasket AND the intake manifold gasket were not torqued properly, it is possible that coolant is leaking into the cylinders causing the random misfires. Your coolant level would tell that story or your possible loss of coolant. As well, the plugs and / or bottom of your radiator cap will tell the story too.
Again, I doubt that you have a sensor problem since you don't have a sensor code identifying a particular bad sensor. (Having said that, I have seen exception.)
Finally, don't rule out a fuel pump. Generally, on the Rendezvous / Aztek, the fuel filter is so large it won't restrict fuel enough to make that much of a difference. Having said that, I replace fuel filters on my 3.4 every 100K. I am at 225K on my Rendezvous.
One more thing, verify that the egr valve can cycle. I partially leaking egr valve will cause your symptoms... but then again should trigger an egr code.
Please keep us all updated and we will continue to assist with additional details.
