Why is my car underpowered going up hills and on the highway.

What is your question?

Sometimes hesitates or jerks when you hit the accelerator. The motor doesn't shake at idle but will sometimes dip below 850ish RPMs but still runs and then it will slowly go back up to around nine hundred. Check engine light will come on every once in awhile and power will stay steady until about 3000 RPMs and then it falls flat and I have to bury the pedal to the floor

What makes this problem better or worse?

You don't really notice it until you hit the highway or go up a hill

How long has your 2001 Hyundai Santa Fe had this problem?

I just bought the car