BA take 767s to places like Phoenix AZ from Heathrow, so they must be capable of taking off with a full fuel load! I think that the .cfg file for the Posky 767 overdoes the drag element, making it almost impossible to reach cruise speed (at FL310, I've managed to get to M0.72 with the default Posky settings) instead of M0.83-ish. If you cut and paste this into the .cfg file, replacing what's there (back up the original first!):
[flight_tuning]
cruise_lift_scalar = 1.00
parasite_drag_scalar = 1.00
induced_drag_scalar = 1.00
elevator_effectiveness = 1.00
aileron_effectiveness = 1.00
rudder_effectiveness = 1.20
pitch_stability = 1.20
roll_stability = 1.00
yaw_stability = 1.00
elevator_trim_effectiveness = 1.0
aileron_trim_effectiveness = 1.0
rudder_trim_effectiveness = 1.0
and then add this as a new section:
[jet_engine]
thrust_scalar=1.05
This should make it behave a little better. You will still need to burn off fuel at FL310 as otherwise the nose gets too high, and once the fuel level is down, you can climb and get a more reasonable attitude.
