I’m flying from KJFK [New York] to UUEE [Moskow]. I just departed and am now flying at 26000ft after decending from 33000ft. I did this because the B777 was going full thrust above 26000ft.
Whenever you increase the speed using the autopilot, the throttle automatically goes to full. It’s unrealistic, but there is nothing you can do except manually adjust power.
You also may have been climbing too fast, and your autopilot tried to maintain your speed. With a long flight like that, you could be too heavy.
That’s issue right there. The faster you fly the more fuel you’ll burn on shorter period of time. The B777 flies at M0.84 typically.
Also flying 345kts will decrease the range you can fly since you are pushing the engines to burn more fuel for a faster speed with a load factor to consider as well.