A340 unable to reach CRZ level AND speed

[tnst05]

Hi,
Departed VTSP with almost max weight. Performace was okay and in limits. After takeoff climb was slow which was expected. Initial was FL300. But (no Derate) the Aircraft made a level off at around FL245. After almost 6 hrs the aircraft is unable to keep the speed and the level. Thrust is at Max Climb (even MCT or TOGA didnt help a lot). So flying around at FL305 6 hrs after Takeoff and speed is around .765 and it cant get faster or higher. After trying to reach normal speed with toga, aispeed decreases.

MSFS 24SU4
V.1.0.5

VTSP-LSZH
Block 101500kg

ZFW 157900

TOW 259,4

at GW 200t max FL300-303
Speed is hanging around at .76

I know climbing with max weight takes time.... but it should happen somewhen.