My father is dead and I'm my father's only child. In the state of Tennessee what do I need to do to get his truck in my name ?

Assuming the truck is paid off and that your father was not married at the time of his death, you can file an Affidavit of Inheritance form with your local tag office.  You can get the form at the tag office or download it at the Tn Dept. of Revenue site.  Take the current title and a certified copy of the death certificate. Of course, you'll need to your own ID with you, too. GI-4 - Inherited Vehicle - Title/Registration Process – Tennessee Department of Revenue