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[RallyxB]

I have a 2002 Toyota Sienna. At 79910 miles the check engine light came on.
My scan tool came up with the following trouble codes:
* P0420
* P0420 P

I took it to the Toyota dealer, who said the problem could be:
* Oxygen Sensors (about $150 each, X2)
* Catalytic converters ($1700)

My brother thought it might be bad gas (or the 10% ethanol in the gas) causing problems, so I added "Lucas Oil Deep Clean Fuel System Cleaner" to a full tank of gas and reset the check engine light.

The van ran great and the check engine light stayed off for 310+ miles.
With less than a 1/4 tank of gas, I refilled van with gas at HESS. Drove for 152.7 miles, then the check engine light came back on.

Used my scan tool to reset the check engine light at 80450 miles to see if it comes back on in 310 miles again or sooner.

Questions:
What could be causing the problem?
A bad sensors I could understand, but I always thought a catalytic converter should last longer than 80K?

Any advice would be greatly appreciated.

Thanks!