What causes hard shifting in low range to mid range? on 2004 Kia Spectra

Check engine light codes are 420 and 455.Problem gets worse as car engine temp reaches normal.

Asked by for the 2004 Kia Spectra
You probably have a plugging and failing cat. converter or bad o2 sensor for the p0420 error. The p0455 error is either a loose gas cap that needs replaced or a leak in the evap system. Look for cracked or loose hoses or vacuum noise or fuel smell in the system.