it won't ride as smooth (it'll ride like any other car you've owned/driven in [unless you've only driven in cadillacs & licolns]
) and the tires won't tuck in quite so well. there is no electronically controlled leveling/suspension system.
once everything wears in though, you probably won't SEE much of a difference. the feeling will never be the same, but oh well. i put the strutmaster conversion kit on my car, a '94 STS. $650 for the parts, $300 for the labor at a local midas. www.strutmasters.com
, see if they have a conversion kit for the SLS.
definitely get the car diagnosed prior to doing anything. i'm not 100% sure what those codes mean aside from that my car also had them, and the dealership quoted me $3500 to fix. could be a lot cheaper for you though, depending on exactly what is occuring.