Exhaust Headers for Chevrolet Silverado GMC Sierra (2003-2006) 6.0LHigh Flow Shorty Exhaust Headers for 2003 2006 Silverado & Sierra (LQ4 LQ9 GMT800) Who is it for: Designed as a direct bolt on replacement for restrictive factory exhaust manifolds, these short tube headers optimize exhaust scavenging to increase low to mid range torque and horsepower without altering the factory catalytic converter placement. The Stock Silverado & Sierra Exhaust Manifold Flaw The factory cast iron exhaust manifolds on GMT800 trucks