If, and if, the reporting is true it is unbelievable. Forgetting to raise the landing gear is, fair enough, a mistake that can happen, not professional and all but it can happen. It is the part afterwards that is astounding! No, or badly done, after take off checklist. Aircraft barely climbs, only reaches fl240, presumably on full power. They cruise like that for an hour and only after fuel is getting low they divert.
If things like that happen and your engines are working it screams "drag". Either flaps, gear or structural damage and you do not proceed towards your destination without knowing what it is.
There must be more to it than what is reported,