No I did it on the downstream. your upstream is what does all the work downstream just tells it if the cat is working properly or not. I'm getting around 28 mpg right now so its good
I had my EGR valve replaced, and a month later had the air intake replaced as well as the spark plugs. I just got another "check engine" light. I believe it might be the PCV valve and I'm going to have the serpentine belt replaced as well. Will keep you posted. I've heard "check engine" lights light up pretty frequently on high-mileage Pro5's any other comments (160K here)
