This is a 1977 Ford F350, sold as a single cab with dual rear tires on a Dana D70 axle. Although it's called a 1 ton truck, the gross weight limit is around 5 1/4 tons. As an upgrade, an airport outfitted it with a set of stairs so it could be used to access private jets.
The mod consists of three versions, the base stage, stairs stage, and flatbed stage.
Majority of stuff (model, textures, physics): Me, Stereo
Some physics and general advice: mclarenf1papa.