Fuel Problem

I have replaced everything on my restoration of my 69 Camaro. The problem is that I can only put in 5 or 6 gallons of gas at a time. When the tank is full it reads 3/4 of a tank on the gauge and is out of gas at 1/4 of tank.. However there is still gas in the tank even though it runs out of gas. Any ideas??
-Matt

It sounds as if you have the wrong tank or sending unit assembly. The pickup is not reaching the bottom of the tank, and the float is not getting it's full swing F to E.