misfire and CES light

I have a 97' tahoe 5.7L 4x4 with 216,000 mi on it, this mourning it began to drive rough with the "CES" light flashing on and off. No problems before so I had AutoZone check the codes. I was told there was a misfire in cyclinder 7 and the O2 sensor on bank 1 before the cat was malfunctioning. The O2 sensors have never been changed. My question is do both O2 sensors before the cat converter need to be changed or can I do just the one? Also I'm gonna be doing a tune-up (plugs, cap n rotor, oil n filter, fuel filter), what else should I look for so the engine will run smooth again. I've checked vaccum hoses and pcv valve, all is good with them.

1st thing is to cure the misfire. Most o2 codes are generated by a poor running engine.

Also tell us what motor? In the future, we need code numbers (Pxxx).

The engine is a 5.7 L Vortec V8. How would you go about fixing the misfire. I checked the plugs from the other cyclinders and they look to have normal wear for a high mileage engine (scorched and dry with a light smell of burnt oil). Also I didn't ask for the code # from the guy at autozone and all he told me is what I've described in my post...rookie mistake I know.

quick update, I changed the plugs, cap n rotor, o2 sensor on left bank pre-cat, and the fuel filter. still idles smooth so no change there but upon giving it gas the engine doesn't shake as violently. Before when giving it gas the truck shook hard. How would I check the compression and the injectors...never done either before.

did you replace the wires?