When on a dealer lot, pickup trucks, especially HD ones, really hold their value. So much so that 1-2 year old used ones with ~20,000 miles are often right at or more than list price of a new truck. (Of course when you're trying to trade one in, it's worthless and you should just scrap it.)
Do you "save" $50,000, OR are you buying an old truck and getting $50,000 less value out of it? You're looking at a 10+ year old truck to find one priced $50,000 less than new. Around here with the GM's that means the body is shot.
When you do come across one that is priced like you think it should be, what's wrong with it? Been down that road a few times. That "too good to be true" deal, usually is.