I have two (2) 1500 Siverados with 5.3 gas engines and automatics. The '02 has 420k miles and is now relegated to towing our 3-horse trailer. It's had the trannie rebuilt at 250k, the differential at just over 300k; at about 350k she wouldn't hold oil pressure at an idle; my mechanic replaced the oil pump and timing chain - she runs like always.
My 2018 Silverado 1500 has towed nothing, but I haul lots of hay with it - 163k and not one problem. Not one.
The '02 has a 4-speed auto, the '18 a 6-speed. Both are good for 20+ mph empty.
Buy new and maintain would be my advice, especially since used trucks are nearly as expensive as used ones.
420k on a gasoline engine is truly impressive.
Common with diesels, but not for a gas engine.