Service engine light that comes on all the time

This is very typical of high-mileage engines. Cylinder compression begins to reduce, due to worn engine components, and the engine generates additional heat under load.
If you are certain that everything in your cooling system is ok, it may be time to consider an engine overhaul.

time for a rebuild or replace

Sounds like a fuel pressure problem. If the light was on it still has the code stored in the ecm. A good shop can check the code and fuel pressure.

Plugged fuel filter? Going up hill will demand more fuel so maybe the filter is restricting high flow.

I had the same problem. Found out it was the code for the wheel bearing

Hold down the "trip" and "trip reset" buttons at the same time when the service engine light comes on. The service engine light comes on between 5000 and 8000 miles as an oil change reminder, however you have to reset it manually.

I can only relate this problem to those similar to Ford F150's,,,on the fords it would be bad grounds from the battery to the frame,and engine,,and from the engine to the Firewall.
This would play havoc with the ECM especially when it was damp.
So i can only suggest the obvious to me at least.
Good luck to you.

i know the camp verde hill of which you speak , last vehicle in the shop with that same scenario , after doing everything possible including a catalyst check , as we could not duplicate the problem , we replaced fuel pump at owners request and next trip he confirmed it was a fix .

There is a button on the right side of the dash if your looking at the steering wheel.
Push the button again and should turn off the power light.

This is an option for climbing hills or when you need a little more from the motor.

The check engine light could mean anything. If the car is running ok then continue on your trip and when you come to an Autozone or Advance auto have them hook up their protable scanner to your Kia's ecm (computer) and they can tell you what the code is and how to fix it.

Don't panic and enjoy the rest of your trip.

Need to ask them what the code was?