The 2008 GMC Sierra 1500 is available as a 2-door, 3-seat regular side. Starting at $31,610, the 2008 GMC Sierra 1500 SL 4x4 Crew Cab 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 18-mpg on the highway. The top of the line 2008GMCSierra 1500AWD Crew Cab , priced at $ 42,210 , is powered by a 6.2L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 12-mpg in the city and 18-mpg on the highway.