2000 Chevy S-10 poor running

2000 s10 4.3 v6 vin code w. Recently changed fuel pump, harness, filter and so on. Also did complete tune up of plugs, wires, cap, rotor, coil, and ign module. Ran fine for about two days. Now have problem of it starts great and runs fine for about 10-15 mins and then it begins to chug and lose power. When it starts to do it, it will idle or accelerate up to 2000 rpm just fine, but when you give it anything more it begins to chug and then dies, even backfires softly at motor. But if you shut it off and wait a minute or two, it runs ok for a few more minutes. Popped code that says left bank o2 sensor, but people tell me that either change all of them or it's the maff sensor? Guy at parts store unplugged maff sensor and it STILL ran horribly. Will a fouled o2 sensor make a vehicle run THAT bad? And do I have to change all of them or just that one? Thank you