Auto Parts: replacement springs, blown fuse, horse drawn carriages

Question
I have a 2002 GMC Envoy with weak springs.  I hate to replace them with the same type of spring.  Do you know of any stiffer spring that would fit this car, either used or new.  Possibly a pickup spring?

Answer
    The Envoy bears no relationship to any truck.  It is a unique design shared with Chevrolet.  The rear suspension is a leaf spring with airbags to assist.  The airbags give the vehicle a self-leveling feature.  I don't know why you are saying that the vehicle has weak springs.  Did you try to tow something and it pushed the rear end down too far?  I might wonder if the air bags are functioning properly.  There is a height sensing switch, an air pump, and the bags themselves.  Any of these could fail, causing the whole system not to work.  This might give a ride that felt like the springs were weak.  So, you need to get the air bag system checked out.  It could be something as simple as a blown fuse.  You have to remember that the towing capacity is not very high on this vehicle. anyway.  Since there is a leaf spring on the back, it's possible that a spring shop could make you a stiffer spring.  But it will ride harder, and mess up the balance between the front and the rear.  It might even be possible to replace the air bags with sturdier units that will hold a higher air pressure, but that would be expensive.  Having springs made at a spring shop is usually very cheap.  The steel leaf spring is the most low-tech car part in existence, they were using them on horse-drawn carriages in the nineteenth century.