99z7153

I have a 99 Z71 ext cab. The rear speakers shot. The dummie at the stereo shop sold me 6.5" speakers to replace the factory(4x6?) rear speakers. I also installed a audiobahn bass tube under rear seat. I modified the opening for the larger speaker. They blew in no time without even pushing them. I went back and got a better pair and they gave me bass blockers to help increase speaker life. I tore the hole mess back down and replaced, five mos later blown again. Would the factory style speaker be better? I would appreciate any help, since putting speakers in the back of a three door is such a pain. I am still using stock head unit. Thanks!!!