Hi! my car is a 2013 ford fiesta hatchback 1.6NA 5MT

It has tons of miles by the previous owners, current at 13.6K

It drives perfectly fine on low to medium speeds; u can't even tell its 13.6K

BUT

when driving on the highway, it looses lots of power when doing climbs.

The engine would shake when I press gas when climbing at about 60mph; you can definitely tell it looses power.

I did downshift to use lower gear to accelerate, but I think the engine power is still limited.

The ignition timing gets retarded by a lot when the climb and shake happen (shown on my obs reader).

(idk if this is normal tho)

I think it is the computer lowering the engine power to protect something?

Or there is something wrong that needed to be fixed?

Thanks!