ml320 altitude sensitive

This may sound crazy. My 2000 ML 320 will have the engine codes #1 bank & #2 bank running lean. I live at 3200 feet in the mountains of NC I can drive off the mountain and clear the computer codes (2) and no check engine light as long as I/m off the mountain. As soon as I go home, check engine light comes on with same codes. Have replaced all 4 O2 sensors, air filter, spark plugs, and the Mass Air sensor. No difference. Any ideas? Engine runs normal just check engine light on. Trying to narrow it down and avoid a trip to the dealer if possible.
Thanks in advance.

if the fuel pressure is ok, return the air flow sensor and get one from the dealer. Seriously aftermarket sensors suck.

need help with this ML 320 that will not stop beeping. it does not sound when the SUV is not moving.