I'm a Business Manager at a GM dealership and I can tell you that ALL of our deposits are refundable. If my customer needs/wants his/her deposit back, I haven't done my job or in RARE cases that emergency you spoke of that was unforeseen showed up.
Either way, I can sell that truck. Period. They're just playing' footsies with ya and hope to make a quick grand regardless.
I would walk in and demand to see the GM/Owner. If they give you the run around, Tell them you'll wait there until they arrive. Make sure to put up a stink about how you're spending $50k and they don't seem to care about that.
Then, I personally, would order the vehicle, let it be delivered and then WALK from the deal and take my deposit elsewhere. Have that dealer do a locate and go get the truck you ordered in the first place...
....Just a thought.
Anyway, any respectable dealer would not ask for a NONREFUNDABLE deposit period.
Good luck!