Trouble Code P0171 System too lean (Bank 1)

Car is not running so great. Loses power under high demand, almost like a rental car that has a governor on it. Any thoughts would be appreciated.
2000 Sentra manual trans.
60k miles

have you had the recall work done on the crank position sensor? I have a P0171 code and the shop's telling me to replace the Mass Air Flow sensor, but I don't believe them because of <a href='http://www.obd-codes.com/trouble_codes/generic/p0171-system-too-lean-bank-1-oxygen-sensor.php">; this code's explanation</a>. Did you ever find out the exact problem?

for the code r&r upstream o2 sensor.

replace the mass air flow sensor. not the o2 sensors