98 Cavalier hesitating/bucking

Recently my 98 Cavalier, 2.2 L, has begun hestitate and spit back through the intake manifold when it's under heavy acceleration, usually around 3K RPM's. When this happens I've noticed that dashlights and headlights will vary in intensity - get brighter/dimmer - very quickly. The engine runs very smoothly without a miss until it gets to that point. It usually doesn't last too long and sometimes I've been able to make it stop just by turning the car off and back on.

Yesterday morning when I left for work it had very little power and wouldn't get above 15 mph, but again runs smoothly without a miss, so wouldn't seem to be a misfire or fuel injector issue. My guess for what happened yesterday is most likely a clogged catalytic converter - the mechanic I took it too thinks so as well, I should find out today when they check it out. But, if it is a clogged exhaust, what would that have to do with the lights fluctuating intensity when I was initially having the problem under acceleration?

Any ideas? Thanks.

FYI - the problem was a clogged catalytic converter. Not sure why that seemed to effect the electrical system with pulsating lights, but replacing the convereter seems to have resolved the issue completely.