i didnt read all the posts, but i vote you keep the trailblazer til its paid off or you are no longer in the hole on it.
My parents did what you are trying to do. They bought a dodge ram a while back, on loan, and had nothing but bad luck with it. They were under about 5 grand on it, traded it in for a year old ford super duty, and thought they were gravy.
Now, they are under on the truck some ridiculous amount. I mean, they love the truck they have now, but they are under much more and dont really have the choice of getting a new vehicle until the truck is paid off.