The factory speakers suck, thats just the way it is. The base radio system comes with a plastic tweeter that's partly covered behind the door panel. And GM puts the other speakers behind the seat. SHEESH!! Then they want to charge you extra to buy the Bose name which is probably another poorly designed cheap system.
I'm in the middle of a complete stero upgrade. So far have installed Kenwood Flipscreen/Touchscreen DVD, Polk 6.5" component speakers, Infinity reference 4" speakers, Kenwood Powered subwoofer,Kenwood 4 channel amp, Sirius, Kenwood Music Keg. Still need to install the Navigation module, and tie up alot of loose ends. The new system sounds awesome. It has taken me 34 hours of installation time so far, and I probably have another full day ahead of me. I mounted the tweeters as a surface mount up on the door panel by the door lock. That way the highs are close to the listeners ear without getting lost to road noise.