The 2004 GMC Sierra 1500 is available as a 2-door, 3-seat regular side. Starting at $21,180, the 2004 GMC Sierra 1500 Base 4x2 Regular Cab 6.5' Box is powered by a 4.3L , 6 -cylinder engine mated to a manual transmission that returns an EPA estimated 15-mpg in the city and 21-mpg on the highway. The top of the line 2004GMCSierra 1500Work Truck 4x2 Regular Cab 8' Box , priced at $ 19,645 , is powered by a 4.3L , 6 - cylinder engine mated to a manual transmission that returns an EPA estimated 15-mpg in the city and 21-mpg on the highway.