97 Grand Marquis codes P0171 and P0174

Just bought a 97 GM w/148,000. Next day Check Engine Light went on and had temporary loss of power. Code read P0171 system lean on bank 1 and P0174 system lean on bank 2. Installed new Fuel Filter. Fuel pump pressure reading 38. Suspected dirty Mass Air Flow sensor. Cleaned it w/MAF Cleaner. All seemed good until the next day. Check Engine Light came back on after about 25 miles, this time P0174. Should I assume faulty MAF at this point? Or should I be looking at something else?

btw starts rough if the morning is cold, starts fine the rest of the day. Haven't experienced performance problems. Had the code cleared after it was read, came back 60 miles later.