I have a 2003 Chev Silverado 1500 HD, which was Turned upside down

I'm sure it is, I didn't have the opportunity to exam it too close, as I was waiting on insurance, then next thing I know, it's towed 3 hours away. Going to look at it this week, so wanted to make sure what to look for. Figured I'd take extra fluids with me (oil, brake, steering, anti freeze), but I really don't expect or fore see any frame damage. Just wanted to make sure what I check before I turn it on, so I don't do any additional damage.

Not possible to damage the engine on the starter. If it was running and locked up, then yes it could be damaged. First thing to do is get in touch with the insurance and get the car BACK TO A LOCAL YARD! If it was towed without your permission, then it’s on the tow company to get it back. If they refuse to, call the police and file a stolen vehicle report. Happens all too often where insurance companies hire “insurance friendly” companies that will move vehicles on a whim to try to get a cheaper storage rate, then jam it up your butt on the tow bill to get it home hoping you will simply abandon the vehicle and they have a free car after 30 days. You should be fine to start the engine if it’s been back upright for a while. Just do as suggested and check all fluids. And that includes the battery. Even “sealed” batteries have a vent for expansion.