(Work in progress)
Introduced in 1955 has a round fender ford truck, In 1958 they changed it to a square fender ford and there was a lot more options. Then in 1968 they change the cab to a dodge style truck and jeeps and other vehicles were introduced through out the 70s 80s until being discontinued somewhere In the 90s when Hasbro made the basic dump truck a part of the "classic steel series"
Keep note that the 1940's style GMC cab-over and Metro Van body styles are also related to the scale of these series.
1950's trucks are worth and e.z 30 dollors in any condition and some sell for 100-200. Newer trucks 68 to 71 sell for a decent price of 30 to 50 bucks depending on condition, If a rare set it could be worth depending on how much the buyers are willing to pay.