The tires come aired to 80 pounds from the factory so they don't flat spot from sitting and for purposes of transport as previously mentioned. When the dealer PDIs your truck they are supposed to air them down to the door sticker. Good dealers do, poorer ones don't. Have to ask yourself, if they miss the tire pressure, what else did they miss on the PDI check list.
Here is a link, this specific one is for the Duratracs I run, same size as yours, but you can find other makes by scrolling down to the Tire make list and click on yours.
https://tirepressure.com/lt275-70r18-tire-pressure
My truck sticker says 65 rear, 60 front, I run 50 (chart says 10,720 load split evenly on all four tires) all around based on the loads I carry and at that pressure I am over max GVW. I could drop to 40 all around for everyday use based on my normal loaded weight.
I get a low tire warning from the TPS every time I start the truck and the yellow tire warning light is always on. The dealer is not allowed to change the TPS limits. You can reset TPS limits with Alpha OBD but I have never bothered to get one, and the security cable that you need to run it.