Well,
1: the AOA at high load can be 5 degrees. And that is why heavy airplanes do not start cruise on FL390, instead around FL300, and they use the stepclimb: climbing higher only as the weight decreasing.
2: FS uses abnormally the fuel. Normally the fuel is kept in the wings, but FS uses the wing tanks first. On the A380 model, the Inner Wing Tanks are called Center1 and Center2, so the amount appears nicely on the Ken Mitchell fuel display. The Center3 is probably recognized as Trim Tank by FS, and (nicely) it remains full as long as possible.
The real A380 have a totally different tank configuration, that a simple FS model could not simulate. It does not have Center tank at all, it have only 2 normal Wing Tanks and a Tip tank per wing. BUT. It has also "cache" tanks too inside the wing, where the fuel is pumped first and the Engines are fed from these "cache" tanks. The capacity of these tanks are added to the others, so in reality the 81000 Gallons are spread into 2x3 Wing tanks, 4 Cache (Feed) tanks and 1 Trim tank
