P0420 bank1 convertor low effienciency. Check for exhaust leaks. No engine misfires present or any other codes present? I'd replace the convertor. Honestly it'* not that uncommon.
P0455 evap system has a large leak. Check for power at the vent valve connector. If a scanner is handy command the valve open and close with a test light to verify the circuit is good. Have also seen fuel tank pressure sensors flake out causing a bad reading, making the Ecm think there is a leak. Best overall test is having the system smoked to check for leaks. Also check the fuel cap seal. Any small cracks will cause a leak.
Last edited by chevy82; 12-28-2014 at 10:11 PM.