Dear,
You can easily follow the Below Route as I did it on my Mehran 2011 along with my Family from 29th May - 14th June 2015
Islamabad - Abbottabad - Mansehra - Besham - Pattan - Dasu - Chillas - Gilgit - Hunza
Fuel : Available in Besham , Two Petrol pumps in Dasu first one at enterance of Dasu other one is after the Bazar , From Gilgit lastly u can Refill for Hunza
Road: Condition till Besham is Good , Besham till Pattan is Average with Plus - Pattan till end of Chillas District is very Bad
Suggestion : Lahore to Abbottabad (Day -1) , Abbottabad to Gilgit (Day - 2) , Gilgit to Hunza Next Day
What I Did on my Mehran : Islamabad - Abbottabad (Day -1) , Abbottabad to Gilgit Next Day - left Abbottabad 04:20 am in Morning reached Gilgit at 09:30 PM. with almost half an hour stays at Major Cities.