There are a lot of variables to consider, what kind of machines do you have, what kind of trucks are you washing, how fast do you want to wash, what system are you going to use, how often will the trucks be washed, etc....
Not trying to avoid your question but there are some things to consider before choosing a truck wash soap.
There are a lot of vendors that sell almost the same thing and the price can vary up to 3 times the price between them.
There are a lot of vendors that sell garbage and will lie to you in your face to sell a product.
There are a lot of products that work ok in truck wash bays and automated systems that will not work good out in the field so understand that there is no "this soap will wash it all" out there, there are some good soaps but some are too strong sometimes and most are too weak all the time.
Tell us more about what you want to wash.