the issue you will have, is since the audio system only sends low frequency to the door woofer, you would want to go with a component setup. but this requires a more exensive speaker. now, there is no harm in putting a coax speaker, but you should disconnect the tweeter (of the new speaker) because sometimes it hinders sound quality. the amplifier in the truck also serves as the crossover so you are limited to the sound quality you can get. if you want to put in a 5x7 replacement you can try jl audio tr570 or alpine sps517 or maybe the spr68 (if it fits). again, not the best way to go, but it will work
