RealmCenter

I have a somewhat odd situation going on. I bought my '01 Trans-Am 6-speed with 72k on it with a massive vacuum leak at the intake/lower plenum. I smoke tested the crankcase after replacing the seals and found it to be leak free. I have put about 1k miles on it with the short terms swinging perfectly however the long terms have always remained higher than I'd like. Yesterday it started consistently flagging lean codes. I induced a vacuum leak and watched the short terms shoot up immediately. Seeing as how it was picking both banks I kind of eliminated the upstream O2s as suspects (I put fowlers in the lowers, the poor running condition for who knows how long weakened the catalysts causing 0420 and 0430). I headed over to Advanced and picked up a MAFS and swapped it in the parking lot. My long terms began dropping on the way home (about 3 miles). They are down from +24.3% to about +14% on both banks in that short drive however it feels like I lost a significant amount of "seat of the pants" pull. This may be a figment of my imagination? I didn't want to clear the ECM memory because I wanted to monitor the change. I did also pick up a new fuel filter while I was there that I haven't installed yet. Any thoughts on the potential performance loss?