pss777 is REALLY heavy

The darn plane can't pick up enough speed before it reaches the end of the runway to takeoff safely. I adjusted the trim and the flaps and that helped BARELY. Next I cut the fuel from 100 percent to 50 percent. That also helped BARELY...what is going on? I see 777 and videos of them taking off all of the time and they use up maybe half of the runway. Can someone tell me what I'm doing wrong? I think I might have to adjust its fuel and payload even more but you would think that it would still be able to takeoff with a reasonable amount of runway left with max payload that it is suppose to be able to handle......By the way the pmdg 747 can takeoff with full fuel and payload. Why cant the 777?