CEL popped on the other day just after getting gas (coincidence?)...anyways, I grounded the SCS wire and it flashed the code for P0133 "Primary O2 Sensor Slow Response"

Since it wasn't a critical code, I reset the ECU...drove to work (35 miles @ highway speed) the next day w/ no CEL...then on my way home, CEL popped on 5 min into the drive (same code)...reset ECU again, let it idle for 10 min (no CEL) then went for an easy drive (40~50 MPH) and the CEL popped on within 10 min...

From all of this, the problem seems a little erratic...not sure if I should keep driving it for a week or two to see if it clears itself?...or bite the bullet and replace the front O2 sensor?...any thoughts?

Background: the car is an '06 w/ ~22k miles, never a problem with it before this, only engine mod is an K&N FIPK...