I am a frequent visitor to Pir Sohawa, been driving on this road when it was almost no road there from Datsun 120Y to Khyber to 2005 Xli, to 1.6 and now CVT-i. D works great uphill and D3 downhill on a conventional AT and flappy peals on Grande.
I seldom take my cars out of Islamabad so can't say anything about it, but for Pir Sohawa road, right from Margalla Road and up to where road ends D all they way works for me.