Toyota Repair: P0420 code, emissions test, firestone service center

Question
I have a 98 Camry with a recurring P0420 code that I am looking for help with.
In February Emissions testing could not be conducted due to this code being set. Testing facility was a Firestone Service center.  Service center replaced the Cat converter and one of the O2 sensors. After replacing the parts the car was driven nearly 3000, mostly highway, miles over a 1 month period. During this period I did on two separate occasions attempt to drive at speeds and duration required to reset the computer to be able to allow an emissions test to be performed but on repeated visits to the emissions test facility they told me that they could still not perform the test. On the 4th such visit they had a state inspector sign off on the test. Two weeks later the check engine light came back on with the same code again. Brought the car back and they said that the replaced converter must have been defective and so did a warranty replacement of the Cat converter. After this second replacement I did not make an attempt to drive the required speeds and durations to reset the computer. Most of my driving to and from work is all highway speeds. Now nearly 9 months later the check engine light is back on again with the same P0420 code. Any suggestions?
The warranty on my repair paperwork says 6 months or 6000 miles however in looking into this issue on the web I have seen that Cat converters have 8yr/80000 mile guarantee. Is this 8yr/80000 only for parts from initial manufacture or does it include replacement parts as well?
VIN 4T1BF22K3WUxxxxxx
Mileage 167800


Answer
The V-6 engine has two converters one for each bank, one is near the radiator and is part of the exhaust manifold the other is near the firewall which consists of the pipe that attaches to the exhaust manifold and contains the main converter and the rear cat converter, so there are actually three converters, two main and one sub, were all of them replaced and if not can you let me know which converters were replaced so far? Also let me know if it's california spec or federal/canada, check the label under the hood. The 8/80,000 warranty is required by federal emission law from the manufacturer, replacement cat converters may have different warranty periods depending on the replacement manufacturers warranty policy.