My cats are clogged, I'm more that certain, truck came from snowy weather, I'm throwing downstream O2 sensors and I'm averaging 14.9 mpg while driving like I just got out of the Alzheimer's unit. Here's my question, do I absolutely HAVE to weld the free flow cats onto where I cut the old ones off? I mean it's past the main o2 for fuel so it shouldn't affect air/fuel mix. Can I just use exhaust sealer and JB weld with a rubber boot clamp on each end of the pipe?