Service engine light... could be O2 sensor

[Mach1]

Hey guys, i just hit 90k a little while ago and lately (under hard acceleration) the motor stumbles. I checked the servce manual for a diagnosis for the hesitation, and the first thing it listed was O2 sensor replacement. And now, the service engine light just came on last night. I tightened the gas cap just to make sure it wasn't a fluke and it seems that it's not. So have any of you guys had this problem and was it solved with a new O2 sensor? Also, I have the V6.