I have a Bassani exhaust, and ever since I had it installed about 6 months ago the truck feels heavier and sluggish. It doesn't feel like air is flowing freely through. I had it checked out a few weeks ago and was told the driver's side header is cracked. Also my check engine light has come on now and I'm starting to get a rough idle. Is this all due to the header?The dealership told me that it could be the exhaust or the engine but they would charge me to look further into it. The truck just doesn't feel like it did when it was stock. Has anyone else had this problem?

 

Bad oxygen sensor maybe?

 

are you saying you have the bassani short headers or are you talking about the stock cast iron header?
But I think SpankDog is on to something..........

 

The header is also Bassani. I've also thought about the O2 sensor but wasn't to sure, If I recall correctly my father and I were looking for the crack and along the way we had disconnected it for a better view. I've checked for fit and it's on tight. Is there a certain way it's supposed to be put back on?

 

It just screws back in, the the plug goes on. This got me thinking that maybe the truck is in Limp-Mode, to make it back home. Didn't say the miles on the truck, but if its over 50K, it might be worth it to buy new O2 sensors. They are pricey.
Did you try and pull any codes from the computer. If you don't have a scanner, I understand AutoZone will do this for free.
Hope this helps