Back speakers can't handle bass

You need to replace all the speakers in the truck except the front tweeters if you have them. I replaced all four with new infinitys from futureshop. Installed it was near 500 dollars. You need to get 2 ohm to match the infinity deck if yours is infinity. Most other systems are 4 ohm, these are 2 x 2 ohms for 2 and 4 ohm use. the factory's are garbage and use paper cones. The rears have plastic caps holding the tweeters in. On all four the paper was ripped away from the magnet and it caused them to vibrate and shake, once replaced with 180 watt infinitys...great sound.