O2 sensor

[4x4banger]

My truck seems to be running a bit rich and I'm thinking it might be time for a new O2 sensor (150,000+ miles on this one). I have a 2 part question.
1. Is the O2 sensor a likely cause of this?
2. Are there good aftermarket brands to go with, or is those one of those things you should buy from toyota?

[82yota]

An O2 sensor can make your truck run rich yes. One went on my grandpas 92 and it got so rich that the truck wouldn't start without a new one when cold for some reason. Changed it and it started right up. When the bad one was in it really smelt like gas.