These days most new vehicles sold in America don’t have major reliability gaps vs other makes sold here. If you are buying used the way that the prior owner(s) used/abused/maintained the vehicle will have much more impact on overall reliability vs. the initial build quality anyway.
That said many vehicles sold in the US are specific to this marketplace and as such if you do have a problem in another country without a good service network for that vehicle you may run into costly and untimely situations getting things fixed if it is related to some odd USA only part. You may want to choose a vehicle based on this to ensure if you run into issues in Peru, Chile, etc that there are dealers/repair shops that support that vehicle.
Also if you are just buying the vehicle for this trip are you doing a loop and driving back to the US to resell the vehicle? If not you probably won’t be able to resell the vehicle legally in South America as your entry visa for the vehicle is for tourist travel only without legal permission to leave or sell that vehicle.
I would ship back to the US or ship elsewhere. In South America, I would probably do more than just the PAH and loop back to Cartagena or Montevideo. The plan is to take my time and it possibly won't even leave North or Central America for a couple of years, there is so much to see.
I would avoid any American truck except the Ford Ranger if you’re going outside of the US with it. But that might just be me, who doesn’t want to either look like a rich American or a drug dealer in other countries. At least get something old and beat up looking if it has to be such a big truck.
Other than that, I’d recommend thinking about usage, like shipping and insurance for such an oversized vehicle, can you get from bed to driver’s seat without going outside, can you spend time inside in halfway comfortable conditions, can you get parts in the countries you’re traveling to.
Just think about this one: people travel with old Land Rover Defenders all over the world. One of the least reliable vehicles. But it’s simple, small, lightweight, with a roof conversion works like a tiny RV with the option of living space inside and a way to the driver’s seat in case you want to leave quickly.
Requirements for world travel are different than outright reliability, size, etc.
