Should be quieter if anything, considering the manifold gaskets "should" be new. If it sounds abnormal take it back and have them fix it.

 

So if it is louder it might be the manifold gaskets? What are some other possibilities? It sound like its coming from right below me when I sit in the drivers seat, but it could be from infront of me. It also just sounds much louder in general when hearing it outside the truck. Its really strange. the idle is really rough when I start it up, and then i quiets down as it runs. Also to note it is very cold up here in northern Maine right now. If i just sit and its idling, and i hit the gas a little it will quiet down, then if I let go of the gas it will wind down, then just open up to a loud idle again. Any thoughts?