Help with struts and shocks.

I have a 2008 GC SXT with the towing package and self-leveling rearend. I have the Sachs Nivomat shocks in the back, so my questions are;

do the Nivomat go bad? If so, can I replace with regular shocks? Since I have the Nivomat in back are the front struts special or are they regular struts?

Thanks for you help.