The hood latch on these can be a problem. The release arm is long and has a couple of bends in it and when they get dirty, rusty and worn sometimes they won't open.
I speak from experience.
This is what the GMC Latch looks like.
GMC Latch You can see two of the bends in my picture. If you can hook something over the lever between the hood and the grill you can then pull the lever (to the right in this picture) to release it. You may be able to attach a stout string by working from the grill, and then passing the string up through the hole.
I've used a couple of skinny screw drivers to position some gas welding rod in place, and for a while I had a nylon wire tie in place because I had so much trouble. Today that truck does not have a hood latch at all. Since its in yard art mode for a few years, that was an easier solution.
