i didn't read the entire thread, but i would replace hoses with aftermarket and get a rad flush.I have a 2012 Ram 1500 with 126K miles. I went on a business trip for 4 days leaving the Ram parked for those days. When I came back I started the truck and the smell knocked me back it was strong. This chemical smell only really happens when the settings are on "Fresh" air and not so much in recirc. There are a lot of good possible fixes in this thread! Hopefully I can find one to work.