2002 Dodge Caravan P0171 SYSTEM TOO LEAN Bank 1

My check engine light came on and I scanned the code. It shows a P0171 (system too lean bank 1) and I did some research. Most online resources list MAF sensor, vaccum leak, low fuel pressure, or O2 sensor as the problem. This vehicle is not equipt with a MAF sensor, instead it uses readings from the MAP sensor. I could not locate any vaccum leaks (i sprayed starting fluid around vaccum lines and mating surfaces between the head, intake, etc. I also replaced the fuel filter, which was original. I then reset the light and drove the car 21 miles before it came back on. When I checked it with the scan tool, the code P0171 was stored again, but the only rediness monitors that had been run were Fuel System, Comprehensive Component, and Misfire. All others were still set to "Not Ready". The best I can come up with is either the fuel pump/regulator (it is all one assembly) or an O2 sensor, or a MAP sensor. Anything will help, please and thankyou!