2001 GMC Sonoma is misfiring again

The misfiring occurs at idle, and whenever I’m driving it. It runs very roughly. You can feel the excessive vibration while you’re just sitting there. I have the 4.3 liter V6 for an engine.

I noticed it was idling a little funny last week - it normally idles at 500 RPMs. Every so often, it would drop a couple hundred RPMS and bounce back - nothing dramatic, but something I noticed.