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.