V6's are great.
I saw a best of 34 mpg out of mine.... with some basic mods
The 3.8 L is a VERY strong engine... trust me, of all people who would know, that would be me
The only video of a v6 w/ magnaflow I could find is below..... but here are the mods:
Cam, Pacesetter headers, Car Sound cat, LT1 I-Pipe, Magnaflow muffler
So, it will not idle so rough.... and not so deep... but I hope this helps you.
http://members.cox.net/landrperformance/lcompcam.wav