You said you replaced the pre cat but what shape is the cat in? Exhaust leak, low on power, bad idle all could be signs of a cloged cat. Just a thought. Also, when you do spark plugs on an aluminum head make sue you use anti seize on the threads or you will have a few other blown out spark plugs. I found out the hard-expensive way. I needed a new head.

Good luck, Dennis

95 Sportage, gone but not forgotten.
98 Jeep TJ, 4" Zone springs with RC Long arms, Ford 8.8", 4.56 gears & Detroit locker rear, D30, 4.56 & Detroit Trutrack front.