Brand confusion
My wife found some info at pixar.wikia.com
Type of Vehicle: An Old North American Tow Truck or a 1951 International Harvester L-170 "boom" truck with elements of a mid-1957 Chevrolet 3800. One-Ton Wrecker Tow Truck. He's also a Hook and Rope pick up Tow Truck. He's a dodge Tow truck too. Hes a mix breed of truck. Gender: Male (most defiantly)
It goes on and on with all kinds of great information about Sir Tow Mater.