i had true duals on my 97 4.6, cut the y pipe off ran 2.25" pipping all the way to dual flowmaster 40's out the rear corners with 3.5" tips. Sounded incredible. Very loud rumble at idel. You could here hte cam lifters like a hot road since there was no crossover.

On my 98 i had true duals run this time, but with shorty headers, new 2.25" piping to x pipe, to dual flowmaster 40 DF's (need louder) out the side like the lightning. Sounds pretty good, has a good rumble at idle. But not loud enough for me.

 

i agree with these guys, go for it. mine sounds great true duals to 40s with 3x22" tips. about the size of pipe, depending on your year model you may already have 2.5 on there already. my 06 did so i just stayed with that size.