Have a friend with a 2008 Taurus Limited with the new 3.5 V-6. It won't go over 45 MPH. Took it to a dealer and had diagnostics run. It's showing number 1 coil pack is bad, so replaced ALL the coil packs, per their recommendation, and nothing changed. O2 sensor was replaced also. Anybody? The catalytic converter is good. Exhaust has no leaks. Any suggestions? Please? Help?

 

Could you tell us how it was determined the catalytic converter(s) is/are good?
As you know if there was a coil misfiring , it does affect the converter especially if it has been run like that for a while.