Does sound fuel related initially, although if the MAF sensor is dirty you could possibly have similar symptoms.
When you travel up hill the engine is working much harder at a given throttle opening than on a level road, therefore more fuel/air is required. The ECU will adjust fuelling according to the load recognised by the Throttle position sensor / Manifold Absolute Pressure ( MAP ) sensor and ultimately the Mass Airflow Sensor ( MAF ). The maff will tell the ECU the density and quantity of air that is being inhaled by the engine.
Either way, If there is any issue you should be getting a SES light or managment light on the dash.
Eddie