Hello ,whith the confinement i’have ManyTime to ask questions

I’v a 54 1/2ton chevy whith a Gas tank behind the seat
My problems

A. when i’m riding The fuel gauge indicator (a new one)is always in mouvement.
And Parked i’m never sure the gasoline level is correct it’s indicate quite empty but i full it whith only 6,6 gal
It’s not precise enougth
Is there any modern Gas tank sender unit fit whith this old tank or other solution ?

B: My consumption is about 29 liters per 100 kms (9,74 mpg)What do you think about?
(Engine 235 cu)
Best regards Frenchie chevy