I do not understand what you mean by idling high? You do not mow with the engine at idle. Now if you mean the engine is at PTO speed and it is increasing its rpm's by a small amount when you start going up a hill then I will assume the governor is doing its job and increasing the engines power when the extra load of going up the hill is encountered. If you mean the rpm's are increasing a crazy amount then I would say you have a bad governor.