98 Malibu misfires when hot

I have a '98 Malibu with 130K miles. For some time now, the engine will misfire when passing or going up grades but only after I have driven it 30-45 minutes. No check engine lights , no codes. As soon as I ease off on the gas, it runs normally, until next time I need extra power. Fuel and Air filters have been changed as have the plugs. I've also put in a few cans of injector cleaner over the past 6 months.

Any thoughts?

Thanks,

How old are the spark plug wires? I'm also thinking maybe Ignition coils or Ignition Module.

the wires and plugs should always be replaced together and only AC DELCO parts. are you getting any pinging ? is the car running hot ? i think the analog temp gage should be in the middle, 180°:confused:

It does sound like spark blowout from either wide gaps of weak ignition.

Sounds like changing wires is a good start. Easy to do.

The engine runs at the correct temperature, no ping, runs normal at approx 2500 rpm on the expressway until it acts up then rpm is 3000-3500, as soon as I let up on the gas, runs normal 2500 rpm.

Anyone think it might be catalytic converter or muffler getting partial plugged? Is there anyway I can test for that? They are both original.

Thanks for the suggestions. I love this site.