Well check with the place you bought it from, some will remedy some issues. As for the lean issue, probably the wide band o2 sensor. They usually only last around 70,000 miles it seems. I would not worry about that much as unless it is VERY lean, you will probably be ok. My mazda is like that and I just leave it and enjoy 35 mpg. It never overheats or has any other issues. But it is up to you.
Rear wiper is probably something electrical but hard to say without more description.
The top end noise could just be cause of the type of oil. Try a quality oil like castrol or mobil1 first.
My father in law has a trailblazer and from what I know, has never had any major issues and it has something like 140,000 on it.