My gas hand is staying on FULL until the tank is a little less than half empty, and then the Gas hand just falls to 3/8 -1/2 on the guage.
Will this be a problem with the guage it self, or in the tank?
Good bet it's the sending unit and the resistance. Just got through replacing mine. There are methods to testing your gauge and sending unit separately for troubleshooting. Check out the threads by doing a gas gauge OR gas tank search.