I have a '98 ml320 and am wondering about changing the shocks & struts.

No bad tire wear, though noticing on wavey or bumpy roads I feel the truck sort of bottoms & tops out. I am noticing this most is when I cross this specific area around 35 mph +. On smooth road & curvy roads ride seems to be smooth & normal, and I have no control issues other than the above mentioned.

Question then is at what point are the ML shocks & struts pretty much shot. I am at 140K miles, running on 4 year old Michelin tires and have very even wear with lots of tread left ( front & rear ). Is there a change out rule of thumb, or will it be quite obvious when the time has come.

Advise appreciated.