I have an RV on a 2005 chassis with 55,000 miles. I find the ride quality to be a harsh. Is it normal for the shocks to need replacement at this low mileage? It used to be American cars needed replacement at this point, but I've found MB shocks to generally hold up much better. I'm running Michelin LT All Season radials and the pressure is to specs of the chassis. I'd hate to spend the money on shocks for no result. It has air shocks in the back.