My 97 F150 w/ a 4.6 L engine threw a P1151 code today. Just a few days ago, I also got an P158 code about an O2 sensor fault. My question is are the two codes related, and if so, how do I find and replace the O2 sensors. The truck has about 128k mileage and to my knowledge still on the original O2 sensors.

I also noticed today that the overdrive light on th end of the shift lever was blinking. Also related?

 

Codes 1151 and 158 are related.
Lack of Ox sensors switching.
The general reasons include harness wiring faults,
intake air leaks, excess fuel, leaks in the EGR system.
There are a host of possible reasons that can generate this code.

I would start by going over all the vacuum lines and rubber on the intake and all parts after the air meter.
Check fuel pressure, possible leaking injectors, harnesss to the OX sensors etc.

Usually intake air leaks show with codes like 171-174 etc but this case there may be other reasons because the PCM is doing other things as well, so the reporting code can be different, but for many of the same reasons..

The OD lamp flash is reporting a transmission fault and should have it's own reporting code.