Or you could crawl underneath the truck (if you don't see or the previous owner hacked the wires off) and look at the tag on the rear differential. It will either say 3L73 (3.73 gearing with limited slip) or 4L10 (4.10 gearing and limited slip.) Hope that helps.
What does this have to do with towing?
He wanted to know how to tell if he had the tow package and that was one of the ways I know how to look for it.
You have the towing package, and no, there isn't trailer brake provisions wired in, you will need to add a controller.