Double Towing with my rig (pics updated 5-13-2014)

If it was a factory installed hitch, it should be rated by the manufacturer. Mine is 3,000 lb / 300 lb tongue weight.

If it was home made, just have a hitch shop look at it and see what they think or even a weld shop. We had hitch shop build a custom one for our rig we had a while ago to tow a boat. It was square tube stock butt welded to angle iron bolted to the frame, with angled pieces welded here and there for support. I think it was stronger than the frame.