Long story short i bought an 05 frontier LE. Drove it home about two hours and got 18-20 MOG. Later in the week it got a misfire code- turns out the catalytic converter had gone to mush. Hallowed out the front passenger and both back converters. A month later I’ve been averaging 13.5-15 MPG every day. Not getting any 02 codes but think of changing the front two out. Any ideas on what’s going on? Is it worth changing the front 02’s any way?