The 2003 GMC Sierra 1500 is available as a 2-door, 3-seat regular side. Starting at $19,362, the 2003 GMC Sierra 1500 Base 4x2 Regular Cab Short Box is powered by a 4.3L , 6 -cylinder engine mated to a manual transmission that returns an EPA estimated 16-mpg in the city and 21-mpg on the highway. The top of the line 2003GMCSierra 1500SLT 4x4 Extended Cab Long Box , priced at $ 31,752 , is powered by a 5.3L , 8 - cylinder engine mated to an automatic transmission that returns an EPA estimated 15-mpg in the city and 19-mpg on the highway.