If you don't have the Bose system, then you have a lot more options for speakers because you can get most anything that fits and is 4 Ohm. The Bose speakers are 2 Ohm. Replacing these with 4 Ohm speakers will cut the Bose amp's output in half, which is opposite what you want.
It has been proven here plenty of times before, but adding sound deadener will do wonders for stock or aftermarket speakers. Sound deadener will quiet down the road noise the speakers are trying to overcome, resulting in perceived higher output as well as give the speakers a better environment to play in that increases their bass response. The deadener will also quiet down the cabin for those times you're driving with the radio down or off, giving it more of luxury car feel. Member DJ (
@08HoeCD) was asking if he should go with JBL or Kicker speakers and ended up not replacing the speakers but adding sound deadener. Here's his thread:
http://www.tahoeyukonforum.com/threads/jbl-vs-kicker.92614/