[Truckbuck]

So I have this code for a lean exhaust that comes on after I drive on the highway for more then 45 mineuts, and once its on it turns off in a few minuets and then comes back on a few minnets later and continues to do this for the rest of the drive no mater how I am driving, even if I am parked it will turn on and off randomly.
Also when the light is on, the drivablitly does not change at all then it was before the light.
I have checked the fuel pump, O2 sensor and looked for vacume leaks with no luck. any ideas?
Its for a 93 chevy C1500 V6 4.3L and it has about 150,000 miles on it.
Thanks for any help!