i have two codes po135 and then it says po135 pending and po155 pending i have 82,000 miles on it are the 02 sensors just old or is it because i haves lts or something

 

It's both. LT's cause O2 sensors to run cooler. Then, you get heater performance codes after a while because the heaters are working harder to keep the O2's warm. Since they sound like they're the originals, I'd say swap 'em out for some C5 rear O2's and ditch the extensions.