VandykeT/A

I've got some Bosch 02 sensors in my T/A and they're about a year or so old. They've been through leaded fuel (I know) and open headers a few times so I'm starting to question them. I've had a very light part throttle miss for the last year or so and its only at part throttle. Here lately its gotten worse I've changed coils, plugs and wires are close to new. Whats the odds the 02s are causing the problem and not tripping a code? Is it possible? I'm clueless as to what the problem could be.