What would cause a car not to shift gears when going up a hill then start a clicking noise?

Typical causes would be:

-faulty throttle position sensor

-faulty accelerator position sensor (if drive-by-wire)

-faulty throttle body (if drive-by-wire)

-restricted exhaust catalyst or other exhaust restriction

-restricted fuel filter

-poor fuel quality

-floor mat interfering with accelerator pedal operation

-overdue for tune-up (gasoline engine only)-ignition timing fault

-knock sensor inoperative

-false low MAF sensor reading

-false MAP sensor reading

-DPFE sensor or hoses bad (Ford only)

-clogged air filter