2000 Ram Van OBD ll Light on - Running Lean!!

On my 2000 1500 Ram Van 3.9 liter engine, the OBD ll light came on and I took it to Autozone and they told me the engine was running lean. They told me it could be an airflow sensor, O2 sensor or even a vacuum leak. I checked everywhere for a vacuum leak but could not find one. Now I don't know whether to change the MAF sensor or the O2 sensor. The van runs but doesn't have alot of power. It idles fine but when in park, I give a lot of gas on hold the throttle down it surges real bad. I just gave it a tune up with plug wires,plugs,air filter,distributor cap,distributor rotor,and wanted to change the fuel filter but I found out it doesn't have one. Its built in the fuel pump!!
Any one have any ideas???
Thanks,
Ricky Newman

did they say what exactly the code was, like a P0300 or something like that? It wouldn't hurt to change the oxygen sensor, it's recommended at 50,000 mile intervals to change them out b/c they wear out and cause driveability issues, similar to what you are experiencing now.

OBD II Light goes out sometimes but still stalls out sometimes while driving. It even backfires a little.You can push the pedal to the floor and it will barely go. Reset computer by touching pos and neg battery grounds together for 30 secs, but did not help things. The only thing I think it could be is the ECM or Fuel pump. It does not have a fuel filter the parts people tell me, its built in to the fuel pump.

2000 3.9L ram van Conversion