When I first start my truck, the exhaust has a strong gas smell to it. When I last inspected it, they said it almost failed the emissions test. It is a 99 V6 with 127k and original ehxaust and o2 sensors. Is this a sign of the cat going bad or the o2 sensors going bad? The truck runs fine, and well, my mileage sucks because of the 35's. Any help would be great, I dont want to fail my next emissions test.