I also have the extended warranty and have done the intake and exhaust (cat back anyway). At this point, I have pretty much decided to do the base mods like the MM IRS kit, subframes, lowering springs or coil overs, diff brace, shifter, etc. Also, talk to Rick @ Earnhardt Ford in Tempe - he is my service advisor (already had warranty work done there) and he told me all the mods I could do without voiding the warranty, even broke out the FRPP catalogue and pointed out some items. Did the guy in the Mach have a lot of track experience? What were the ET's of each car?