My SES light came on yestersday, but when I started my truck to go home I knew something was wrong before the light came on. it runs rough, lacks power. Took it to advance and got the codes: PO156 02 sensor circuit malfunction / Bank 2 / Sensor 2 .
Underneath that code was PO307 cylinder 7 misfire
If I replace the O2 sensor will that fix my problems? or are there 2 different things I am looking for?

( PS the SES light blinks or flashes when going up steep hills on interstate)

 

The blinking mil means severe miss probably cyl #7. which might account for the downstream 02 code. check the coil, plug, and if your truck is a 05, you might have an injector failure. I've had a few issues with injectors on 05's.

 

I have a 2000 4.6 manual trans. It has 114,988 miles, replaced the plugs after 110,000.
is the sensor before the cat or after the cat?

 

The O2 sensor is not your problem, the misfire is. IT is most likely a bad COP. Move the COP from cylinder 7 to one of the front cylinders and reset the comp. Then when the Code comes back see if it moved to the other cylinder. If it moved the COP is bad, if it didn't the injector is most likely bad and you can move it around too.

Cylinder 7 is the 3rd back on the D. side.

 

Disconnect your negative battery cable and then replace the C.O.P. as stated 3rd one back on the drivers side. Bank 2 sensor 2 is the O2 monitor on the drivers side behind the converter. Disconnecting the battery while you replace the coil should clear the codes, if the P0156 code comes back check wireing and connectors before replaceing the sensor.