Want to tow with a tow bar a K2500 pickup with a K3500 from NH to AZ. Are there any regulations across country to do this? Dollies are expensive. Has anyone done this? 
I personally like to have more of a weight advantage between my tow vehicle and the towed vehicle. But I think it is possible, and I've seen trucks towed behind motorhomes.
I recommend you hook them up and drive around town a bit to see how the rig works. Some vehicles, because of their steering geometry just don't track well using a towbar. So give it try locally before hitting the road.
As far as towing laws, the only requirement is a DOT approved tow bar rated for your weight, and working lights on the back of the towed vehicle.
Good luck! 