Looks like Torsion Rod for tailgate lift assist.
https://www.ramforum.com/threads/installing-4th-gen-tailgate-on-a-3rd-gen-truck.99700/
Mar 7, 2017 at 6:23 PM #3
chrisp2493
"The last thing to do is deal with the torsion bar on the bottom if it came with one. The one end of the bar has a slot...