I have a 1998 Ford F150 4x4 8 cyl 4.6 check digit W 125,000 miles. I had not noticed any problems, live in Maryland, had to go thru required emissions testing and they said the check engine light was not working and the bank 1 oxygen sensor behind cat was mal****ioning. I replaced the check engine bulb and the O2 sensor and it ran fine until I got 225 miles on it and then the check engine light came on. I went to Auto Zone and they checked it on the hand held tester and came up with code P0420. I notice the truck seems to be "holding back" some and this code could be catalytic converter replacement time, my local shop says $1200.00, the other O2 sensor is $54.00 on the passenger side. I have straight pipes now from the cat back already invester $700 in exhaust manifold on passenger side 6 months ago, I am just wondering if this code is a definite on the converter or I should try some others things first?