I can't think of any "national" chains that do emissions repairs. You could check your local yellow pages for automotive repair shops that specialize in emissions work. Or, you could google, "emissions repair _______" and fill in your local town/city. That should get you some useful search results.

 

I replaced the two O2 sensors in front of the cat, and the 1 I could find behing the cat.

ALL codes were cleared, with the exception of Fault Code P0155. People keep saying there should be a fourth O2 sensor on the truck(96 F150 4.9 I6) but I can't find it.

Is there a map anywhere of the 96 F150 4.9L I6 motor and its oxygen sensor locations?