06 f250 obd po420?
 

Just bought 06 f250, 5.4, cel came on last night po420,truck running like crap,no power, in gear at idle feels like its gonna die, need help, thanks

This code could be like opening a can of worms.
Do you have the tools to remove the oxygen sensors? If so you might try removing one of them (closest to engine) and then start the vehicle and see if there is any difference.
What you are doing is allowing the exhaust to exit through the sensor opening to bypass a possibly clogged converter. If that makes a big difference, replacing the converter is only part of the correction. Need to know if misfire was a problem and go from there. There could be MANY reasons for excessive rich mixture that might have contributed to a melted converter. Sooooo,we take things one at a time.