My bro has a 97 3.8 RS and tells me it has a miss/hesitation after leaving work and immediately getting on the onramp and when standing on it, it hesitates. He doesn't mention it doing it in the morning coming on the hightway, but maybe I figure it has more warm up time from his house in the morn, than when leaving work to the onramp.

Changed the fuel filter and checked the tranny cable to make sure its all lined up and was loose before, but this prob. persists.
I'm maybe thinking Opti-spark going but not there yet, not sure if the 6'ers had the Opti but maybe plugs too but should seem to do it while warm as well. Also changed the PCV and now it idles irractically till warm then smooths out, I think IAC valkve but could be too that the PCV cover plate not 100% sealed and now has minute vaccumm leak.
Any help???

 

It very well could be a vacuum leak somewhere. I would check plugs and wires first.