Run ability

I have a 1993 Jeep Cherokee that all of the sudden
developed a no power situation and it will start and
run but when I go to give it gas it dies tries to die
out spits and sputters it doesn't stall but it just has
no power no get up and go it's throwing one code
which is 51 I get to 12 which is the PCM power
then I get the 51 which is rich condition then I get
55 which is end of message from all accounts and
purposes that I can find online people are telling
me that this is a O2 sensor problem I don't want to
go out and spend 50 bucks on an O2 sensor and
come to find out it's something else any
suggestions would be greatly appreciated