I feel your frustration, on a lighter note, don't drive slow vehicles.
Seriously though, although difficult (especially for me) best thing is to not let your pride override your survival. Just back off or stop. He stops I think you have a reasonable expectation that he intends "great bodily harm"
Yep. Best thing to do at that point is to stop. If he stops and gets out of his vehicle, he is committing a felony at the same time as giving up his best weapon (his truck). As soon as that happens, you have three options, fight (shoot him), flight (just take off), or flatten (run his ass over).