Formula One cars have problems with monitoring exactly how much fuel is
remaining in the tank,
and they spend millions on those cars.  They do not, as yet, have a method
that is accurate enough
for the situations they encounter.

The senders in most automotive gasoline tanks are meant to provide relative
indications of the fuel charge, nothing much more.   You could diddle with
them and improve them, I have little doubt,
but they still may not do what you want.

Exactly what are you trying to accomplish?

It's called the fuel gauge...??

Seriously?  How accurate do you need to be?  You could rob the signal
from the fuel gauge sender, which is just a resistance value.

Is this something for mass production or the aftermarket?

Won't the built-in car computer give you what you are looking for?
Which of the following do you need to know and to what level of
accuracy:

1.  How much total fuel is in the tank.  The precise number of total
gallons remaining at any one point in time.
2.  How much usable fuel is in the tank.  Total number of gallons
remaining less the unusable portion the pickup can't reach.
3.  How many miles you can drive the car based on the remaining usable
fuel and your average fuel usage.
4.  Your average and current fuel usage.

1. and 2. are very difficult to measure precisely without actually
placing the fuel in a container of known size and shape.  It is all but
impossible to measure with a degree of precision because fuel sloshes
around and moves the unit up and down.  Also gas tanks are notoriously
lumpy (polygonal) making an estimate with a dipstick or float subject
to lots of error.

3. and 4. can be estimated more or less by using trip computers
available in most cars.  They too are subject to errors in reading
remaining fuel, as we have all observed.