If you're seeing the battery symbol on the dash, you're actually in 'accessory', rather than 'off'. That's how GM tells you you're in that mode -- by lighting that lamp. If true, it suggests that something is misaligned (I'd guess ignition switch or key cylinder, but let's see what the people who've been helping up to this point say).
The fact that you don't hear the interlock mechanisms clicking when the brake is depressed or the shifter lock engaged is also a problem (and most likely, related). You're able to start & drive the truck, so it's not preventing you from using it.
Next time you're on level ground, and not near anything, I wonder if it would be a good idea to see if you can get the shifter out of park, with the key out of the ignition, and if the vehicle will move, once you do?
There's some risk here, so
don't just go out and do this (if something gets further misaligned, you may lose the ability to start the vehicle (unless you can move the shifter enough to make it think it's in Neutral, if you can't get it back in Park again). And certainly don't do this by yourself -- get the boyfriend to help. If you get the truck moving and can't get back in to stop it, that's a bad situation. 💥
You have a workaround for the time being, with the emergency key release on the column that
@linneje pointed you to. Do you find that you can turn the key back a tiny bit further once you press that emergency release button?