Rick,
When you installed the new radiator, did you install a new thermostat and then fill the cooling system?
Sitting in the garage idling doesn't allow good air flow through the radiator, but it shouldn't make the truck blow its top. My guess is that every thing is actually OK, but that the system might have needed burping. After the thermostat did open, because the truck wasn't moving through nice cool air, it just couldn't cool down fast enough.
I would fill everything back up and head down the road. Take a jug of water, but I'll bet things will settle down and be fine.
Stuart
