O2 Sensor 92 K1500 5.7

[StingRay]

I have a 92 K 1500 with a 5.7. I put a new engine in it about 3 years ago after an oil ring broke on the old one. When I put in my new crate motor I replaced the o2 sensor as I figured the old one had been compromised by a lot of oil going by it. I had already been through the emissions system and had previously replaced all the sensors and EGR and reused those. Since the new engine I have been plagued by code 13. I have replaced the o2 sensor 3 times. It always fails by starting to give trouble as it gets a little colder. I have used AC Delco parts and have been through all of the factory service manuals diagnostics 3 time previously. Every time all I can come up with is the 02 sensor. I replace it and it's fine for about another year. I'm getting tired of this. Does anybody have any ideas if there is any other culprit to look for or are the o2 sensors just that crappy now? They aren't cheap either.