Exhaust systems, cams, unichip, cold air, etc.
I've decided the best mods for my XR6 will be the full exhaust+unichip (hopefully the Herrod setup) and a few more intake mods. That will do until I add forced induction to it. :D
There is a six cylinder performance forum somewhere, but I forget the URL. Not much useful stuff for more modern 4.0l 6s, seemed to mostly focus on the older crossflows.