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Without your model number I am only able to give you general information. This is most likely caused by overheating of the motor. This is typically caused by a buildup of lint and dirt. If your venting is restricted this can cause this issue as well.
If you do not feel confident repairing this problem yourself, then you can have it repaired at your home by a Sears technician. Here is a link for the website:
Sears Home Services
Here is a link that you may use to view the parts list diagram or for parts purchases;
Sears Parts Direct
If you would like specific help with your dryer, please reply to this post with the model number and more details.