Check this tutorial by our awesome friend Brandon, it will explain how to save fuel whilst climbing and in cruise. It seems as you have climbed way too fast or in an inefficient manner and you lost a couple tons of fuel during climb.
To save fuel during the cruise stage of flight I suggest checking it this guide to step climbing by DeerCrusher, it is very crucial to step climb especially in those very long flights that are excess of 7 or 8 hours.
Another great guide by DC for improving aircraft endurance and extending your range. It speaks about the importance of using Trim, etc…
In my opinion, you did something wrong while in the Climbing Stage of flight, as the 777 let alone the 77W can do flights that are 17, 18, 19, even more than 20 hours if you play your cards right and do everything correctly.
I hope the links I provided above can help you, they really did help me when I got started doing Ultra Long Hauls when Global was initially released.