Keith,
There is no time or mileage that dictates the proper time to replace shocks on cars, trucks, or coaches. The only reason to replace shocks is to correct a problem like leaking, worn or broken mounting, or a ride control issue like porpoising. I sold my last coach with 175,000 miles on it and it still had the original shocks that were riding as good as it did at 50,000 miles. Some people like a firmer ride than the OEM Bilstein shocks provide, and for them that is a ride control issue, so they should get Koni shocks to stiffen the ride. But no shock is going to make a road full of pot holes into a comfortable ride.
Gerald