Application Summary: 1999-2005 Chevrolet Silverado 1500 Base LS LT (Bed Length: 78.0 & Bed Type: Stepside & Cylinder: 6, 8 | Qualifier: For Use with Modified Exhaust Systems, with Tail Pipes on Opposite Sides | Note: with Dual Side Exit Exhaust (Left & Right)); 1999-2005 GMC Sierra 1500 Base SL SLT WT SLE HT (Bed Length: 78.0 & Bed Type: Stepside & Cylinder: 6, 8 | Qualifier: For Use with Modified Exhaust Systems, with Tail Pipes on Opposite Sides | Note: with Dual Side Exit Exhaust (Left & Right))