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the normal cause for this is something internal to the transmission unfortunately, which typically necessitates refurbishment or replacement of the entire transmission.
Other possibilities would be a low/degraded fuel, a software/adaptations problem, or other issune with the drive line such as a worn flex disc or problem with the transfer case.
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.