my geo tracker will not pull up a steep hill what could be wrong with it

If the check engine light is not on, have exhaust system flow checked. If light is on, get a free code read at an Autozone and post results to further assist you.

Is it an automatic? If so they just don't have enough power. put it in 4wd low.. If it's standard shift and you can't work the clutch in low then you might want to have it looked it... it's just a problem in the auto's