First Check engine light

As another '95.5 owner, I'm very confident there are not any Tacoma's without OBD2. Toyota knew the requirements that were coming and introduced them a half year before the '96 OBD2 requirements went into effect.
You may hear some contradicting things about that, for an example in my state we have bi-yearly emissions testing and it is a different process for pre-'96 vehicles (not sure if this is how all state emissions tests work). So you may hear that a '95.5 Tacoma does not meet OBD2 standards based upon the fact that it is tested using the same methods as non-OBD2 vehicles. 96+ vehicles are emissions tested through OBD2, a 95.5 will have to be tested on a dyno. That may signal to an owner that the truck does not meet OBD2 (even though it does) because its a different process because of a regulatory requirement based on year of manufacture.

Also, not sure if this will make you feel better or worse about your O2 sensor replacement, but I have had an intermittent P0420 code. I just clear mine anytime it pops up and it wont come back for months. I still pass emissions so I'm not buying a new cat, and it runs great so I see no issue with my O2 sensors.. It may just be a weird thing that goes wrong every once in a while. It might not have even been your O2 sensor you could be experiencing whatever minor issue I also have. Maybe the heater element suggestion from @O'Silver_Taco.