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.

1 answer
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.