I ran into the same thing with my truck and decided to go the whole route and replace the factory stuff with aftermarket. On the plus side, I found someone to buy my factory head unit for more than the replacement.
I have a Vega component set for the front doors and tweeter replacement (door speakers are 6X9 with midrange and tweeters built in, the kit includes replacement tweeters for the pillars). These speakers are rated at 200 watts.
The rear speakers are Panasonic 5" and are a direct replacement for the rear speakers.
Note, when installing your door and rear speakers, you have to rewire the speakers and, please cut out the plastic over the door holes and use duct tape to tie down whats left (can you say RATTLE).
I have two 10" dual voil coil VEGA sub woofers mounted into a box that nicely fits behind the middle seat and doesn't interfere with carrying passengers in the back seat.
The output from the head unit (both woofer and left and right output are fed into a Pioneer 600 watt amp that has input for both the subwoofer and the left/right channels.
My setup might be on the extreeme end of the scale however, I DO like my music clear, crisp and LOUD.
Hope this helps,
Charlie
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Y2K 3500, 4WD, Auto, 3. 54, Custom Brush Guard, Mopar nerf bars & rock guard, Camper package, Towing package, all options except leather, Mopar Rock Guards, Vent Shades, Solar Shade, RoseWood Dash, Air-Lift Air Bags, Hadley 'BULLY' air horns, Rancho RS9000s, Stainless Rocker Panels, KC DayLighters, Lance 1130 Camper