OK, you have my attention. Why do you want to pay much, much more at a dealer rather than walking into Auto Zone, Pep Boys, Western Auto, etc ?
Are we talking about just the rubber part or the metal (sometimes plastic) thingie with multiple flex points that holds the rubber?
In either case, there will be a book tied to the windshield wiper display that allows you to look up what you need OR tell the clerk behind the counter you have a Trailblazer and he will tell you what you need. At the auto parts store you will have your choice of "normal" wipers, enclosed in rubber boot wipers, high performance wipers, dual wipers, etc from three or four different brands.
All the wipers I have purchased lately fit pretty much every style wiper arm so you should not be concerned that your choice will not fit your truck. Where I live Auto Zone offers free, while you wait, no appointment required installation of wiper blades.
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