1996 Chevy S-10 Sudden speed drop.

Driving for almost an hour at 65 mph on cruise control came onto a construction site slowed down to 45 mph. Once past pushed resume on cruise control and nothing happened. Pushed the gas pedal and truck struggled to get to 50 mph. The check engine code reads P0171. System too lean Bank1. I don't know what that means. My son tells me it could be a map sensor or a clogged fuel filter or maybe a bad or dirty fuel injector. I was reading that maybe it's a bad 02 sensor? (Had it changed when the catalatic convertor was changed a year ago). It will start and idle rough, but runs like it is on 2 cylinders when I drive it. Help! Any words of wisdom from the experts would be greatly appreciated. UPDATE: CHANGED FUEL FILTER and INSTALLED NEW MAP SENSOR. STILL HAVE SAME PROBLEM. 2nd update. Took it to the Shop. Turned out to be a bad coil pak. $246.00 later all is well. Thank you for your input. Talked way over this shade tree mechanic's head. Thanks just the same.