It depends on the body style you have, GMT-400 or GMT-800. 1999 was a transition year, and I don't recall how the Suburbans were released, if they were a half-year release, or if there was a difference between the weight classes. 2001 was the first model year for the Duramax. GM has always found a way to defy any direction of logic during these times. A GMT-800 (1999+) would be the simplest, with very little accommodations to consider.