My tow rig for 10 years. 1986 K30 with a 12 valve Cummins and NV4500. I boxed the frame when I built it. It did great towing the 38' trailer with home built living quarters.
I still have the K30 but I found a 2009 F750 standard cab grapple truck that had been rolled. 6.7 Cummins, 3500 series...