97 Suburban PO133 and PO430 codes

Hi everyone, I have a 97 GMC 1/2 ton Suburban (http://www.obd-codes.com/forums/viewtopic.php?t=2958#) 2 wheel drive (http://www.obd-codes.com/forums/viewtopic.php?t=2958#) with 5.7 and 170,000 miles. I bought it pretty resonable about 5000 miles ago with failed intake gaskets. I replaced the gaskets with the new style and while I had it apart also upgraded the Fuel injection unit. I also replaced plugs,wires cap and rotor. It has run great ever since down the road pulling my sons 63 Nova drag car (http://www.obd-codes.com/forums/viewtopic.php?t=2958#). The last couple weeks my Wife has been driving (http://www.obd-codes.com/forums/viewtopic.php?t=2958#) it in town to work and now these codes came up.
Transient DTC Po133
02 sensor
CKT slow response
bank 1 sensor 1
and,
History DTC po430
catalyst efficiency below threshold
Bank 2
Should I replace the sensor first? Or what other tests can I do? I dont know how much the vehicle (http://www.obd-codes.com/forums/viewtopic.php?t=2958#) was driven with leaking intake gaskets before I got it. Could this have ruined the Catalytic convertors? Or the sensors? Any comments or suggestions are welcome.
Thanks,
ccnova

Slow response can be caused by mixture issues, what was done to upgrade the FI unit, yes between the mileage and possible contamination from antifreeze, assuming it leaked into the cylinders, this could damage the cat. Fix the o2 code first then clear the codes and see what happens. Go ahead and repalce that sensor. 1st one on the drivers side bank. See this link for a technical expl. http://service.gm.com/gmspo/mode6/pdf/1998/98t57R_LD_yE.pdf

For the fuel injection unit I replaced the "spider" with the new style that has the injector at each port rather than the "check valve". up till now it was really only being driven down the hiway. The past three weeks while I am rebuilding the motor in my Daughters car my wife has been using it in town. Could this also have an effect or is it just coincidence?
Thanks for the help.
ccnova

No effect as far as the spider unit update or driving habits.

Ok thanks for the help and also thanks for the link!
ccnova