Dear Friend
Let me explain why Diesel SUVs give better mileage.
As you know in Saudi Arabia all the cars are petrol but Heavy vehicles like trucks and buses are diesel why? Cant they built heavy petrol engines for these trucks and buses.
Actually to pull heavier weights it needs more torque and as you know petrol engines have low torque as compared to diesel thats why in trucks and buses only diesel engines are used.
Now coming to your scenario you live in mountainous area I have been to Astore, Rama, Deosai, Skardu, Shigar, Khaplu, Hunza nad way back to Lahore in August 2013 on my 1989, HJ60, 2H, 3980 cc diesel and I did not felt a single problem anywhere. Because diesel are meant for mountainous areas.
You can also witness that in Europe specially mountainous areas even Mercedes and BMW luxurious sedans have diesel engines.
I would suggest to go for 1KZTE preferably manual for better fuel economy or auto for luxury.