Sounds like you still have the stock exhaust manifolds on yet,if you do,you're just wasting your money putting any kind of dual set-up on it.It won't go any faster or get any better milege,as the cast iron manifolds and factory Y pipe are the biggest choke points on a Hemi. Even with headers you're not going to gain much in the way of power with a true dual set-up.Once you get to full bolt-ons with a fairly big cam,even then you're not going to notice much in the way of a power increase from true duals. Save the money it'd cost you to put a mandrel bent true dual set-up on for a set of long tube headers and a good midpipe. Most exhaust shops aren't set-up to do mandrel bends,so there's a good chance to get a decent set-up,you'll have to buy a bunch of mandrel bends for them to build you a good set-up out of stainless steel.Stay away from any shop who tells you crush bends and aluminiumized pipe are good,they aren't,the pipe will rust out in a couple years,and crush bends restrict the exhaust flow