I bought my V8 with 146,000 a few months ago. Soon after purchase I left my wife sit in it (idling) while I went in to get license plates. When I came out, the CEL was on. I had a small OBDII reader with me, checked the code (same code as yours. R and L bank to lean), then cleared the code. A few days later, got on the accelerator a bit, and the same code came up. Checked with VCDS and it read the same thing (both banks too lean). I thought about it a bit and decided that the injectors were not opening enough (maybe the car sat on the lot a while and was not driven much?) (Too lean, not enough fuel, too much air)
I bought fuel injector cleaner, poured it in the gas tank, filled it with high grade fuel, then REALLY got on the accelerator a few times. Standing start, quick accelerate in S mode on tranny. Next light same thing, etc. That was about 2 months ago and Presto, no CEL light since then.