The salesman gives the priority code. Delivery also depends on things like when "OK to buy" takes place. That's 5 consecutive days with no major screw ups. If that happens, the 5 day cycle keeps repeating until they get it right. Meanwhile, all the built trucks sit in lots waiting. If they discover problems that require them to come back from what I've read is they pull them from the back of the line and your order that was first built in the front of the line is now at the back of the line. Realistically, it's not likely many will hit dealers before December.
When did the 2018’s start showing up? December 2017?