Friend. Because of the symptom you are describing, insurance has been displaced in the box, this one when it heats the metals inside its interior and that is how it produces the effect you describe.
I recommend that you perform several tests to make sure that it is really a cash problem and not clutch fatigue (clutch), since the symptom is very similar.
Pay special attention to the engine revolutions in idle when it is hot and without dynamic load, since if the engine tends to stop the problem it is even greater and may be due to a failure in the axial bearing.
For any questions or queries do not hesitate to communicate with me to the e-mail