My Z has about 96000 miles. About 1 month ago I got a PO133 for B1S1. I reset the computer and the code did not clear. Given the high mileage I replaced both O2 sensors with Delco parts. Now I am getting a PO135 for B1S1. The car has had Hooker LTs for nearly 40000 miles and never threw a code until recently. Any suggestions?

Thanks