A military flatbed truck.
It is built in a cab-over-engine arrangement with two large headlights, a fuel-cell powered engine and three axles. It was produced as a standardized cutaway chassis, which was then, depending on the need of the buyer, modified. As such, two primary models exist - a semi-trailer truck (often found with the accompanying trailer) and flatbed truck. The cab appears to be based off the real-life GMC COE.
The US Army used a great deal of these trucks to transport soldiers and goods over long distances. As Army vehicles, they were painted olive drab bore a serial number in addition to the Army's insignia. Private companies also employed this type of vehicle, though most used the truck and trailer model. Flatbeds were not unheard-of, but were notably less common.
After the war, these sturdy vehicles continue to be used. While the scarcity of available replacement parts (most importantly tires, windshields and engine parts) limits their usefulness somewhat, they nonetheless play an important part in the supply systems of various factions, e.g. the New California Republic, which even has a dedicated truck repair depot at Camp McCarran. The Boomers appear to have several trucks in fairly good condition parked at Nellis Air Force Base.