Do you realize that number of vehicles were designed not directly for use in division but for supplying Army from railway hubs? In distances of Siberia and Manchuria with their railway connections? Soviets used 100 000 trucks for their advanced according to Glantz in 1945! There were probably not so many modern trucks available in Japan at the time. And fuel! How much fuel you will need to transport to support them? That's was one big problem Soviets were chellenging in 1945.
According to Glantz the 1945 Manchurian Offensive had 85,819 vehicles to support an advance across both sides of that territory. Hachi-Go called for one advance against Primorye and than another against Lake Baikal if all went well. Considering that the Kwantung Army's 763,000 men had 29,000 vehicles between them, extending the ratio to 1.3 million gets more than 49,400. And again, what the Japanese lacked the Soviets would have lacked even moreso.