The 2012 GMC Sierra 1500 is available as a 2-door, 3-seat regular side. Starting at $27,965, the 2012 GMC Sierra 1500 SLE 4x2 Regular Cab 6.5' Box is powered by a 4.8L , 8 -cylinder engine mated to an automatic transmission that returns an EPA estimated 14-mpg in the city and 19-mpg on the highway. The top of the line 2012GMCSierra 1500SL 4x4 Crew Cab , priced at $ 35,375 , is powered by a 4.8L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 13-mpg in the city and 18-mpg on the highway.