I know this is an old post but mine started doing this. Mine is an 05 SE 4.0 with 240k. I dont know if the cats or a cat is going out. Mine drives and sounds good while driving lightly but if I use moderate to heavy acceleration the truck feels like its has power loss and the engine makes what I can best describe as a clattering sound while my truck has trouble shifting. My SES light flashes only while doing this and if the light stays on I get P0420 & 430 along with Random multiple misfire detected. I dont know what to do.