Oxygen sensor and EGR vlave

I bought this 96 Rodeo 3.2L Automatic 2WD with >130,000 miles one year ago. From this forum I learned that it is good to use fuel injector cleaner for every gas fill up. So I bought a box of Chevron injector cleaner from costco. After the the second fill-up the check engine light came up with the code for low catalytic converter efficiency. So I stopped using the injector cleaner. The check engine light went away after few days but the fuel consumption went up. Earlier it used to go ~18 mpg, now it goes 11~14 mpg. So asked one of my coworker, he replied me that the cleaner burns the oxygen sensor and catalytic converter. Few days back I replaced the two O2 sensors before the cat. But now again check engine light came up with code 1406 which translates into EGR valve problem. Can anyone please write me why after changing O2 sensors EGR problem showed up? Should I use cleaner?

Thanks

Use injector cleaner every 3000 miles.