99 Suburban service engine light

I have a 99 sub with 79,000 miles the light just came on ran a check and it came up with no specific codes other than random missfire on the # 2 bank. I tuned it about 10,000 miles ago and I replced the wires after the light came on. Ran fine for a day light is back on and it is still showing random missfire and also running lean. All four 02 sensors have been replaced in the last year. The light comes on and off at time and when its off it runs fine also the tail pipe is black and gas millage is way down. The check on the 02 sensors is showing ok they seem to be sweeping up and down. Any ideas?

I have a neighbor who is a mechanic and he claims that if you have a miss and already did a tune-up to check the fuel injectors.