A brochure of the 1999 Chevrolet truck range in Mexico, including the Silverado/Cheyenne.

http://storm.oldcarmanualproject.com/chevroletpickupstrucks1999.htm

The 400SS Sportside is interesting and badged as a 2500. Appears to just have the basic 5.3-liter Vortec V8 by the 255 horsepower output rating.