This is what I did to my 2006 Jeep grand cherokee limited
Not very much, but improved my performance. Im even running 22 inch factory reproduction srt8 replica wheels.
Mods: K&N 77 series CAI, Magnaflow Exhaust, Diablo Sport Trinity "Canned Tune", Jet Flow Throttle Body Spacer, Bosch Iridium Plugs.
Check my vids out!!
I run a 5.62 second 0 to 60 time mostly at night
and a 14.48 quarter mile time