Surely, in level flight at ANY altitude, lift will equal weight ? Since lift and drag are affected by the same parameters, (speed, density etc) the drag is directly related to lift and drag is opposed by thrust.
Therefore, for any given weight and constant mach number, the lift, drag and thrust will unaffected by altitude.
On the 747-400 (GE engines) at a weight of 310.0 kg and mach .86, fuel burn per engine at 39.0 is 2830 kg/hr and at 26.0 is 3175, the 10% improvement at altitude largely due the higher - and more efficient - rpm required to produce the same thrust.
Wouldn't this suggest that the engine thrust was more-or-less the same at both altitudes.................or am I missing something ?