There are two likely issues here. First is that the reluctor wheel on the camshaft is either bad or shifted. Think of the sensor as an eye and the reluctor wheel as the instructions. If the instructions are wrong, the eye tells the brain (the PCM) wrong information, and this can keep the engine from starting. If the eye is disconnected, the brain can use information from other sensors to make a good guess, and the engine can run, though maybe not perfectly.
The second possible situation is that you have a stretched timing chain. This is common on GM vehicles as a whole, though I haven’t heard of your engine in particular having that issue. Ultimately it’s the same eye/instructions issue, but if the actual camshaft is out of position, the engine should be running pretty badly even with the sensor unplugged.
Do these extra holes look a whole lot like your transmission lines? Those could be for the oil cooler circuit, which your truck may not have. If that’s the case, you’re fine to leave them open.