I just went through this with my 2013 Ram 3500. The bags on my truck were aftermarket not factory and because I have had some in older model trucks, I knew they were probably Firestone. I do not have an onboard compressor. If you have an onboard compressor it will complicate a bit to rundown the leak. Get soapy water in a spray bottle like you do to test for propane leaks for your BBQ. Run pressure into the suspension system either max with out a load, or halfway and connect a trailer on it for some weight. Get underneath and spray your fittings and look for the air bubbles. Mine was at the inflation valve fitting. Went to Michigan Truck .Com to buy new valve and changed it out. Problem solved.