So I just finished up a PS pump, Brake Booster and related hose install, looking at what's next. I am original owner 2006 6L Denali w/175K. I have battled the typical P300 code but have never had a Cat or O2 sensor code. I do seem to have less power even after plugs/wires, TB clean but not due to any of that, just degrading over the years - I think. From this forum, I've heard that clogged Cats can impact power/performance & that the rear 2 O2 sensors monitor the Health of the Cat's. Also, in RockAuto, Walker Cat Info states that "Catalytic Converters are designed to last the life of your vehicle – they do not fail on their own" Is that true, the Cats don't fail unless impacted by other engine issue, heat, mixture, poor gas, oil sludge ? If so, When should these O2 sensors be changed, I was waiting for a code - but I've changed on other vehicles way before 175K ? Any thoughts are appreciated - Thanks.