Welcome Gale! It would be helpful to know where the truck has lived it's life...
Here in the dry, arid southwest, mileage and age are of less consequence than they are in more humid places... I have had several trucks with more than 200k on them that were in great condition mechanically and looked good too. My own K2500 has 320k on it at present and I expect to keep it basically forever. My plow truck is a totally rust free '93 K2500 suburban that's running strong at 170k. I just found a nice Dakota for my dad that had 250k on it and it's also doing well, though it will eventually die as he lives in Michigan...
In general, if an engine (and transmission) has made it that far, it's probably had fairly thorough maintenance. If the 3.5L Ecoboost uses cam phasers, it would be good to know when they were last replaced, as that is a very common thing but may be later engines only... It is pretty expensive to have that work done...
The rest of the truck should be fine if it's from a dry environment. My opinion would be that an easy life, good maintenance, and just a tiny bit of luck in not getting bad parts should keep any truck running toward the 500k mark if it's not in the rustbelt. Sure, you're going to replace some things like tires, shocks, wheel bearings, seat covers, but the cost of replacing those things pales in comparison to a payment on a newer truck... If you can do your own maintenance for those sort of things, all the better. Low mileage engines for 11 year old trucks are hard to come by here in the SW, but they're a bit more common in the midwest, where rust took out the truck before it got to 200k miles...
If it's from a place that has more humidity, all bets are off... The engine and driveline may be sound, but wiring, frame integrity, and body structure begin to come into play as major issues that routine maintenance has no ability to overcome...
Good luck!!