The 2020 GMC Sierra 1500 is available as a 2-door, 3-seat regular side. Starting at $29,600, the 2020 GMC Sierra 1500 4x2 Regular Cab is powered by a 4.3L , 6 -cylinder engine mated to an automatic transmission that returns an EPA estimated 16-mpg in the city and 21-mpg on the highway. The top of the line 2020GMCSierra 1500Denali 4x4 Crew Cab 6.5' Box , priced at $ 58,900 , is powered by a 5.3L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 16-mpg in the city and 22-mpg on the highway.