Kenwood and Elemental Designs Install...

2fast4thelaw

Ouch!! Thats a really high crossover setting for a 12" sub plus 18 db/Hz is pretty steep too. I set my subs at 60Hz @12db. It sounds like you need some mid bass up front. Try dropping your crossover points to the fronts and sub to 60-80Hz and it should sound a lot better.

12" subs make terrible mid bass drivers and your sub has a heavy high mass cone which is optimized for really deep bass.

As far as crossover slopes, steep slopes like 18/db and 24/db are best left to mids and highs where fatter slopes give you more overlap for the subwoofer. If you can, mix the two such as running 24 db/oct on your fronts at 60Hz and the run your sub at 12/db at 60Hz. This would be ideal in your situation to optimize mid bass in your car. Your sub will sound much cleaner at this setting and your fronts will give you that punch your looking for.