Hi..
I'm new here and I understand where you are coming from... You may have to crate your dog while you go out so he understands you are the boss and not him...
I have a 2 month old puppy who loves to nip.. he's very intelligent though... I hated like heck to have to get him a crate but finally gave in... Now if he nips he goes to his crate.. I close the door but I don't shut it tight.. He understands that if he bites he goes in there.. I don't have him sleep in there though as he sleeps beside my bed on the floor with his big furry blanket.. he doesn't move from there.. He's a very bright puppy.
As for the truck?? maybe resort to putting him in the very back and get the dog barriers to put back there.. Better to have a safe dog than an injured one..
You'll have to work very hard on showing your dog who is boss as pit bulls have a mind of their own..
Good luck on your endeavours..