Before WWII, Ford and GM had assembly plants in Japan and sold their passenger cars and trucks in Japanese market (more information). IJA purchased many Ford and GM trucks and used them in Chino-Japanese war.
In the late 1930s, the relationship between Japan and USA was getting worse and Ford and GM stopped their business in Japan before the Pacific War. So, Ford and GM trucks were not so many seen in the Pacific theater.
Ford trucks in China Incident