It was a small green orb, the sizr if a fist, hovering and buzzing over the tree tops. It matched pace with the truck. Creeped me out. The with no warning it blinked out.
I realize it's a long ways past when you saw it, but I think I know what your little fireball was. It sounds like ball lightning, both in appearance and behavior. I've seen this stuff a few times, it's WEIRD. It's buzzing the trees due to lightning's inherent attraction to tall things. Sometimes the little buggers will "Chase" metallic objects, explode, "teleport" and pass through solid objects. It comes in different colors and sizes, and is the origin on a lot of ghost stories and legends of angels, demons, fairies, etc.
If you ever see it again, please do try to get a picture of it. It's rather rare, and it's pretty well harmless unless you're holding a metal object or try to touch it.
I don't really have any creepy stories. I have WEIRD stories, but nothing I'd call creepy or scary.