Slant Six Fuel Mileage?

I fueled up 45 miles back and the fuel gauge has dropped from "F" to 3/4 tank? The original owner's manual says this car has a 16 gallon tank, I guess that is correct? We installed a new sending unit 10 days ago and it just seems to be a bit hard on gas. I'll top off Saturday and see what the math says about the mpg on my /6 engine. It just seems like that gauge is moving south in a hurry? Checked for leaks at the new sending unit and it's still dry? Thanks in advance for your input!

Mike

You might not have a 16 gallon tank either.
My Dart was originally a 318 car and it has a 13.
If everything is correct and it does have a 13 you used a little over three gallons or so, and are getting about 14 miles to the gallon.

Just a quick non accurate guess from the info provided, and assuming it's a 13 gallon tank.