i got a friend that wants new spring on his 2002 chevy 3500 dully. he says he wants a smoother ride but still the load/towing capacity

whats a good set of springs/ suspension?

 

well load capacity and ride quality do not generally go hand and hand .usually have to give up one or the other ,but the least offensive way is generally to go with air bags ,better capacity with some better ride ,but you have to maintain a certain amount of air in them at all times .