5/16 to 3/8 fuel line
Tate, check the float level before you do anything.
Now, the sending unit will have to be changed out. Otherwise, the 3/8ths line everywhere else is still sucking through a 5/16 sized line and the problem, if that be it, will still exisit.
You can get 3/8's line from a number of sources. Finelines would be one, year one would be another but expensive spot.
Someone chime in on where to get 3/8's A body fuel line and sender.