As above, get the engine running properly via tune-up services including likely replacement of the O2 sensor (they get lazy with age) and potentially a catalytic converter or two, depending on how your truck was equipped originally. A scan tool will be very helpful. New-to-you vehicle? A cranking-compression test is recommended.
1. High hydrocarbons (HC) is often due to misfire. The entire cylinder-full of air/fuel mix goes out the exhaust valve when that cylinder doesn't fire, and the high HC is the fuel part of the air/fuel mixture. In the process it overheats the catalytic converter causing it to fail.
2. High Carbon Monoxide (CO) is generally due to an over-rich fuel mixture. The air/fuel mixture burns, but not completely because there's too much fuel/not enough oxygen (air). In a properly-proportioned fuel/air mixture, there's enough oxygen during the burn to reduce the CO into carbon dioxide (CO2)
When a cylinder misfires, it forces the O2 sensor to send a false "lean" signal to the computer because all the oxygen (air) in the misfiring cylinder is going out the exhaust valve along with the unburned fuel. A misfire therefore causes high HC, and indirectly, high CO.
Side-note: Since there's only one O2 sensor on the TBI trucks, either the sensor is severely screwed-up, or the misfiring cylinder is on the same bank that the sensor is monitoring. While it's possible that the misfire is so severe that the excess O2 is traveling from the other bank...it's not so likely.
3. High NOx often indicates a failed EGR system. Essentially, combustion temperature is excessive. The more-expensive catalyst systems also lower NOx emissions; but I don't know if your vehicle would be equipped with such a catalyst. I'd be looking at the EGR first, ignition timing second, and other engine-tune issues third.