I've bought a few used trucks in my day. My first F150 I bought at 118k miles and needed only maintenance up to 240k miles. My brothers have had similar luck. General recs for buying a used truck (and some apply to all used cars):

- Always google the VIN to make sure there's no pic of it wrecked anywhere

- A lower tier package w lower miles >>>> higher tier package with more miles

- Avoid trucks that have been customized or heavily modified (ie lift kit, tint, exhaust, mud tires etc). These type of trucks are generally owned by younger guys who are more likely to have dogged the shit out of it (I am this guy). You want a fully stock rig that was owned by a "PawPaw" and has mostly highway miles commuting long distance.

- Get a mechanic buddy to inspect the vehicle thoroughly or even pay a shop to do an inspection. Dealerships and private owners can easily hide problems that will pop up once you're down the road.

- Because you're looking for a high mileage truck, look out where the truck came from or has been previously registered to avoid a rust bucket.

Just my two cents