As some of you know I've been battling an over heating issue with my 91 fox body 5.0 stang. I had new cats and flowmaster muffler installed thinking it was a blockage, time will tell as I have to wait for summer again (Hot months). But I noticed the area between my drivers seat and consul was getting very hot to touch so I took it back to the muffler shop thinking I had a cracked exhaust. After they put the car on the lift they noticed that the passenger side cats changed to a brass color but the drivers side didn't. He then said that something was wrong with the drivers side engine because the drivers side cats should have changed colors to. The front cats were hollowed out. the 2 back cats are new magnaflows. What could be my causing this?