The codes are essentially system too lean on both banks. You either have a fueling problem, a large exhaust leak ahead of BOTH O2 sensors, or a vacuum leak. Whatever the problem, the PCM cannot adjust the fuel trim enough to compensate for the problem. This leads to your next diagnostic steps, which will be to check for vacuum leaks and to verify fuel pressure. Checking for vacuum leaks requires few tools and almost no monetary investment, so it's one of the best places to start. It also nets results more often than not, which is why I suggested it first. On the Vortec motor (or any other MAF system) a "vacuum leak" could be considered any air entering the intake system downstream of the MAF, so you have to check the intake tube as well. If you are absolutely sure that you have checked and rechecked all vacuum lines, intake hoses, plenum and lower manifold mating surfaces, and sensor plugs, then move on to the fueling system. Check pressure and make sure you're within range ( can't remember the exact numbers). If low, pinch off the return line at the braid/rubber portion and see if the pressure comes into range. If it does, you either have a faulty regulator or a clogged fuel filter (if you haven't replaced it already). If it still doesn't come up, it's likely a pump issue.
If everything checks out, then a faulty MAF is possible. These tend to be expensive, so if you have a buddy that has a truck with the same motor, swap em and see if your problem goes away and his truck starts running poorly. If that happens, clean the MAF. If it still runs poorly, get a new one.
