You need to stop the movement of the receiver from going side to side. You probably found out the angled pin will work it's way into the hole as the receiver goes side to side eventually elongating the hole in the hitch. Especially if your using friction sway bars.
I had to replace the hitch (good time for a upgrade) and then went with the Hitchrider. This will stop all movement and easy to install.
I would also recommend not using the angled pin or even the locking pins with cheap Chinese locks and go with just a 5/8" bolt with large flat washers and a Nylock nut.
http://www.hitchrider.com/hitch-vise-gm-2.htm