Have a 99 Suburban. Runs fine except on occasion while both town and highway driving it will "miss" and stumble. Picks right back up and keeps going. Also on occasion while stopped the rpm's will surge up and down about 750 rpm. Started with a new dist. cap, rotor, fuel filter. Checked the tranny fluid. Next came oxygen sensors on the back side of the convertors. Run 2 bottles of NAPA Clean thru with new gas. I have a service engine light on, ran it down to the local shop. They said to fix the O2 sensors. No difference. Still stumbles. Any help would be great. thanks.