$30k for a domestic used truck that has 2-4 years worth of miles and is only $10k cheaper than a new truck that you can get discounts on and lease for pretty cheap? Doesn't sound like a great deal.
I always lease because of all the discounts and rebates you can get on domestic brands, I don't drive a ton and I like getting a new car every couple of years. That, and working at a dealership, I see a lot of people who try to get out of vehicles they bought and are upside down thousands of dollars in a car they don't want anymore.
If you do buy used, I suggest buying a CPO vehicle.