The Karakoram Highway in Pakistan, described as the eighth wonder of the world, is one of the few projects to significantly benefit both countries. With little prospects of the US taking on this role and no other takers on the horizon, it will be very keen to keep China by its side. For China the options are less clear-cut. Certainly in the short term it has nothing to lose by keeping Islamabad on-side, but long term there are a number of issues which could lead to disharmony. These include Pakistan's close identification with the Taleban in Afghanistan.
China has a Muslim problem in Sinkiang.
At the moment Islamic activity in China is largely indigenous in origin, but should this situation change Islamabad would definitely feel the temperature drop. The other potential conflict of interest is India. Since the end of the Cold War, relations between Beijing and New Delhi have improved. With the present global trend stressing on economic development, both realise they have a lot to gain by cooperation. In actuality, though, Beijing will not be able to keep two wives at the same time, especially not two who hate each other so much.