how can i get fuller bass range

Because you either have your crossovers set incorrectly (which you certainly do) or you have a subwoofer enclosure that is incorrectly designed for the speakers you're using (which you may) or you have main woofers that are ineffective or out of phase (which you might) or you have acoustic issues inside the vehicle that are emphasizing the sub bass while sucking out the bass frequencies (which is likely.)  Or any combination of all the above.

The first thing I would recommend is this:

1) Remove any external crossovers from the system

1. done. no avail.

2. done. no avail.

3. done. no avail. how bout hooking up ONE woofer only, and testing it with ALL other speakers off. same response. i hadnt really thought of my main speakers being out of phase with the woofers. that was a good point, but not the problem.

perhaps i will try to video the difference in sound between my car and my roomate's truck and post it on youtube and link it here. i kno the sound quallity will be terrible, but u should be able to hear what i mean if i listed to similar tones in both cars. ill give it a shot. if it seems useful to post it, i will.

my point is this is clearly not a crossover frequency problem. theres a fair chance i DO have my crossovers set wrong. i dont have a meter to properly adjust every octave to make sure they are equal, i just go by ear. your second and fourth points sound like the responses i was looking for help on.

im almost positive i need a box thats tuned differently. ive stated that im bad with boxes, and im aware that boxes have everything to do with sound. im wondering is there a sealed box i can get thats good on high bass, or a ported box i can get thats good on low bass.

ive also stated that 12 inch cones didnt seem to do the trick. i tried at least 5 different brands before i put 15s in and realized that was what i needed. i think this is due to the accoustics of the car. i have a fairly large trunk. interestingly enough, when i tried the 12 inch solo baric L7s, they sounded ok. long story short, i let my roomate borrow the woofers. in his blazer, the L7s EXCELLED.  every sound range was touched appropriately. he doesnt have the lows as strong as i have, but all around his bass is much more full. ive installed a brutus 1500 watt amp for him, much similar to my twin 1200 watt brutus. it sounded SO much better in his truck that i decided to let him keep the woofers, and a few months later we called it even after he gave me an all around brake job.

more so i was actually hoping to not only hear from an expert (and you guys seem VERY knowledgable), but perhaps find someone who had the same car as me and tell me a bit about thier setup.

again thanks for all help given. its greatly appreciated.