A car or other vehicle losing power going uphill can be caused by a few different things however the most common cause of a car or other vehicle losing power going uphill is due to a clogged fuel filter or partially clogged fuel lines.
If the car doesn't get enough fuel to it then it can lose power and it may seem fine going down straight roads without any hills because the car needs less power to do so.
But when you start up an incline and go up a hill the car will need more power and may be struggling due to not getting the proper amount of gasoline or fuel going to the injectors.
Another cause of the car losing power going uphill could be a clogged fuel injector as well or a fuel injector being bad which can also cause an engine misfire.
If the fuel filter and fuel lines are all good and the fuel injectors are not the problem then it can be other things causing the loss of engine power when going uphill.
Some other causes of loss of power when going uphill could be clogged air filter, clogged exhaust, clogged catalytic converter, bad camshaft position sensor, bad ignition coils, bad spark plugs, bad ignition module.