The amount of miles that a Chevy Truck or any brand of Truck or vehicle will last will depend on how well you take care of and maintain the vehicle.
I remember seeing a video on Youtube of a Chevy Truck that reached 500,000 miles and is still going strong so it's possible to make a vehicle including a Chevy Truck last 500,000 miles or even more sometimes as long as you change the engine oil, transmission fluid and oil filter as well as the transmission filter.
If you notice any fluid leaks get them fixed to extend the life of the transmission and engine and take care of the vehicle and it will last you many miles.
A new truck should last you 500,000 miles or more especially since they cost so much money to buy so take care of that vehicle and you should not have any problems.
I have a Chevy Truck that as 300,000 miles on it and so far it's still going good and runs and drives like new so you should get a lot of miles out of a Chevy Truck.