I am sorry if you did not get the information you wanted last time.
As I said then, this model of garden tractor uses an electric clutch, the belt is supposed to be tight at all times. The tractor is designed this way and should have no problem turning the blades, which was the reason I mentioned other common causes of the same symptoms.
If the blades are actually turning so hard they stall the engine then something has been assembled incorrectly. The most likely cause is a belt that has been installed incorrectly or a deck pulley or blade that has been installed without the proper spacers.
Take off the belt and see if the blades now spin freely. If one of the pulleys still does not turn freely then it will be the best place to look for a problem. Remove the blade and see if it still turns hard, if so, then try removing the pulley. If there is still an issue the mandrel itself has a problem and may need to be replaced.