Okay so i just swapped my 3.8L out for a 5.0L V8 in my 91 cougar. everything went well until i started it up and let it run for about 5 minutes, reving it up a bit then go look under the hood and the CAT's are about 4,000 degrees and bright RED. lol i dont know whats going on. i did just keep the stock exhaust from the v6 that was in the could this be why? what else could cause this?