As they say in my neck of the woods and many other places, the bass is in the house.
Mine is powered by a mono Pioneer Stage 4 PRS-1200M. Currently it is not listed on Pioneer's website, but you can still get them at Crutchfield and other places.
IMHO, the best way to improve the bass response correctly is not to try to upgrade the OEM factory sub unless it meets your expectation. Some folks who did upgrade the OEM, later on change it out for something better. Many here have gone to the aftermarket route via the JL Audio stealth box or a custom solution with a proper amp.
Those silly people in charge of the audio department at Chrysler should go back to school.
Best for now.
Laredo X, Trail Rated, QTii, Sele-Terrian, Quadra Lift, Off-Road Adventure Package ii, Nokian Rotiva AT, Tow, AFE CAI, Custom Sound System ( HAT speakers, JLAudio , Pioneer , JBL MS-8 & RF 3.sixty.3 -- see the writeup link below for more details)