Hey guys! I just had a cat back exhaust with 3 1/2" pipe and a flowmaster 40 series installed on my 2004 Durango HEMI. It seems to be a bit laggier when stepping on the gas. It still has power but after 30-40 mph ,the rpm gets way up there before she wants to go anywhere. Taking off is no issue at all. What can I do to rectify this problem. I was thinking cold air intake, cleaning the T.B., spark plugs & wires, and fixing timing