pls91fc

I have a 91 NA that I got in sept. and it was running nice when i got it. I put it in the garage for the winter and started it occassionally. I took it out this spring and it was idling between 500-1000 rpms kinda jogging inbetween, wouldnt stay still. But after takeoff it runs smooth up to about 6k rpm under hard acceleration and then the acceleration slows, like hesitates and takes awhile to reach redline. I was told this could be many things from vacuum leak, cat convert to my apex seals going. I got the plugs, wires and fuel filter changed about a month ago. Does anyone have any idea? Thanks Pat