My Nissan Sentra will not stop over heating.

Your transmission problems are very unlikely related to the overheating. You may Have a faulty water pump. However you need to check the engine oil and make sure there is no antifreeze in your engine oil. If there is then you have a blown head gasket, and or damaged cylinder head. This can also be checked by making sure there is no oil in your radiator. Either would be the same diagnosis. oil and water(antifreeze) separate. So you would see water dots on your oil dipstick. Or you will see oil dots in your radiator. Both would explain your overheating. Water pumps are not that big of a repair. But if you are having transmission problems as well. I would run it through your local public auction.