general maintanence

I'm sure these questions have come up about 50 times, but maybe you can all entertain me:

Has anyone actually followed the "change oil" light as a guide to oil change intervals and driven their trailblazer up to 100K miles? I am actually not skeptical like most about needing to change the oil around every 12000 miles when the light comes on, but choose to change it every 5K as my boss (owner) says to.

Second, the manual is a little vague on the differences between changing the transmission fluid after 30K or 60K. If I dont tow a trailer, drive my TB both in the city and highways, and dont live in a hilly area, can I wait until 60k, or should I just do it at 30K. Same with the air filter?

What is the issue with the brakes in the truck? My brakes are warped after 34K just like other TB owners. Will Chevy fix this problem under warranty, or do they just go for the wear and tear excuse?

Also, does anyone else have the same spongey feel in the brake pedal. It almost feels like the hydraulic fluid is compressing, which I am aware is impossible. And it creeks when I push them down all the way.