The GM 12637647 Updated Driver Side Exhaust Manifold for your 2001-2010 GM 6.6L Duramax features a "full bore" unlike the factory exhaust manifold that is "kinked or dented" for additional clearance.
GDP 01-16 DURAMAX UP PIPE PASS SIDE W/GASKETS
GM LB7 Passanger side up pipe 2001-2004 GM Federal 2004.5-20016 Offroad