I own three cars. the 94 rt-10 rides like my 2004 Cadillac Deville, which I enjoy. My 2006 SRT-10 has a harsh ride. I have already replaced the tires in the 2006 to PS2 which has helped the ride about 40% better. What else can I do to get a smoother softer ride to the 2006 srt-10?