GMC added the AT4 off-road trim to the redesigned 2020 Sierra heavy-duty lineup. We recently took possession of a loaded 2020 Sierra 2500 AT4 crew cab and wondered just how its fuel economy would ...

we averaged 20 mpg. That’s respectable for a buff 5688-pound vehicle. One quirk is that lighter, less luxurious Sierra 4x4s equipped with GMC’s six-speed automatic transmission outscore the ...