Congrats on the Magnaflow, I love mine and it puts a smile on my face everyday and I got it put on in January. After a few thousand miles it just seemed to get better sounding too. I'm glad you noticed a increase in mpg though, I didn't.
However just doing the exhaust won't add that much hp, even the tech at Magnaflow said I would be lucky to see even 1 or 2 hp. I don't know though, maybe my mpg didn't increase though because I love the way it sounds in the 2500 to 3000 rpm range, so I have my foot in it more often lol.
06 Sport Dark Shadow Grey 4.0l
K&N drop in, Scanguage II, Explorer Domelight and ohc
Magnaflow 2.5" catback, metal tailgate handle from graniteguy
Ultra Mongoose 178 rims 16x8 with Toyo Open Country AT II.
Cranked torsion bars
Kenwood head unit, 6.5" Kenwood Excelon components, Rockford Fosgate 10" sub, all powered by 2 Alpine amps.
coming soon: Bilstein shocks , Wet Okole seat covers.