Silverado & Sierra 1 3/4" Longtube Headers & Y-Pipe 1999-06 (4.8L, 5.3L) Mandrel Bent Tubing, CNC Machined Flanges Race Version with "NO" AIR/EGR Fittings, 304 Polished Stainless Steel 1 3/4" Primaries/3" Collector, Standard Graphite Manifold Gaskets 1999-2006 (2wd & 4wd) Gains over 25rwhp Revised Y-Pipe: Now works with 4L60E & 4L80E transmissions. Also allows more room for 4wd vehicles