I have a few that I have found no reference for... Does anyone else have any insight...RPO Code Description The codes I did get were from http://www.princeton.edu/~patrickm/rpo.html Thanx! New to group and have found most of the posts here more appropriate than either of the public 4x4 groups... BTW: '89 GMC Jimmy K5 - 350TBI - 33x12.5x15 on 2.5" lift RPO Cd Description C4B ? C4Z ? C5M ? CMD ? E5Z ? E6D ? E9Z ? SLM ? UP8 ? V73 ? XUZ ? YA7 ? YD3 ? YD5 ? YD6 ? YUZ ? Z75 ? ZUZ ? 83K ?