tranny slip? Misfire?

2000 cavalier z24 2.4 with 112K automatic. This week twice while getting on the interstate i have incurred some problems. It was a steep on ramp both times and it was at the point where im ready to merge into traffic and really get down on it , its like its shifting between two gears. The tach bounces back and forth between around 3k and 4k for about 5-8 seconds then everythings fine. The trans does fine anywhere else. I have also noticed a slight rough idle. Its been like that since i bought it 3 months ago. It kinda feels like a misfire or something b/c it will be fine then it has a slight rough spurt. Nothing bad just enough for me to notice. Any ideas?

oh yeah i forgot to mention that the plugs and wires were replaced at separate times, or so it says in the maintenance records.