GOT SERIAL NUMBER?
I would say Warren may be in a situation where his employer is trying to see if Warren is wise enough to admit to "knowing what he does not know".
The differences between fuel systems can not be covered safely in only a few pages, much less in the space an internet forum/conversation provides. this being an emission controlled truck, the US [and possible state] government[s] have some rules about training that cover who has been certified to repair these units (those C.A.R.B. rules, imnsho, are the excuses dealers/manufacturers are using with an abundance of caution to keep diagnostic and password reset software proprietary/trade secret but I digress).
As it has a 'fuel trim valve' that is replaceable, I assume this is a tier2 truck, as such the 'computer' will not provide fuel or spark under a lot of possible conditions if everything is not within certain pre-set perimeters. you will need to be able to access the error codes, to find out why this truck does not start. does it run if you give it starting fuel?

The hose has to be hooked up to the carb to allow fuel to flow from the regulator. Did you check the carb?