The 1999 GMC Sierra 2500 is available as a 2-door, 3-seat regular side. Starting at $20,892, the 1999 GMC Sierra 2500 SL 4x2 2dr Extended Cab Long Box is powered by a 5.7L, 8-cylinder engine mated to a manual transmission that returns an EPA estimated The top of the line 1999 GMC Sierra 2500 SLE 4x2 Regular Cab HD, priced at $22,988, is powered by a 6.0L, 8-cylinder engine mated to a manual transmission that returns an EPA estimated