o2 sensor replacement question
 

When I did my Hooker LT install the first week of this year, I ran the car with open headers while on the jackstands to bring the engine up to temp and bleed coolant system (I broke the cylinder head temp sensor during the header install). I ran the engine for no more than 10 minutes at a time, but I started it and ran it several times inthe 24 hours between the completion of the header install, and installation of my y-pipe. During the time that the engine was running, the o2 sensors were installed in the headers and connected.

Ever since getting the car back on the road, it hasn't felt like the big difference that many describe. It does feel somewhat better, but it's not the night/day difference that many talk about. The car feels to have actually lost a lot of power in the low to mid RPM range and gained a little up top, however the dyno told a different story. The dyno showed a miniscule gain of 6HP with the headers (while pulling up to 3 degrees of KR). I have since solved my KR problem, and driven the car to a new best that is just over 2 tenths better in the 1/4 mile than before the headers.

The car is pulling fuel at idle, and adding fuel everywhere else. With the BLMs UNLOCKED, the car will add 20% fuel to each bank during WOT because it thinks it's lean. I can't find any leaks anywhere, the header gaskets are still nice and clean, there's no soot gathering anywhere except at a couple of joints in the Mufflex y-pipe.

I have been wondering about my o2 sensors, considering the possibility that they might be messed up or something, but during scanning with Autotap I can see them scan from .100 to .900, although they don't scan back and forth the full range all the time, they do get there and sometimes they go farther than that.

I have a brand new set of GM o2 sensors at home, and I guess I'm wondering if I should bother to go ahead and install them. So if you had GM o2 sensors that were less than 6 months old (6500 miles), and scanned the full range and weren't setting any DTCs, would you replace them with brand new sensors?

There was a recent thread that suggested that the "curing" process that new headers go through after being installed will foul O2 sensors.

So even though they scan the full range, they could still be bad and cause driveability issues without setting a code or SES light?