1. Do not go through New York city.
2. Unload the gun and all magazines. Do not have any magazine inserted in the gun. Put the gun and the magazines in a case and lock it with a real lock. If you take ammo, put the ammo in a separate case and lock that with a lock as well. Put both cases as far away from any occupant in the truck - under the seat, behind the seat.
Watch Busted - The Citizen's Guide to Surviving a Police Encounter before you leave:
Assuming your pickup does not have shell, camper or topper. If it does, the gun/ammo goes in the back, not in the passenger compartment.