I just changed my 2004 with 210,ooo miles 2 weeks ago. It has full synthetic. Not sure what was in there before.
Hopefully it wasn't actually conventional oil. For 2010, GM changed their warranty requirements from conventional to synthetic blend on most engines. I don't know if Nissan did the same around the same time period, but it's likely.
I'm using Pennzoil platinum full synthetic now cause tires plus carries only Pennzoil.. that's fine with me, but was debating on trying 10w40 high mileage part synthetic cause engine was making noise the other day.. but I put more oil in as it was low on oil, it went away.. I suppose there's other reasons to try that high mileage , but I think I'll stick with what I'm currently doing.