Basic Mopar gas guage is a 5VDC meter..
If the guage only reads low, then something with the rheostadt on the sending unit arm is out of tweak.
The arm/rheostadt should have a full swing from about 80 Ohms to 10 Ohms..
As posted above, many of the Mopar replacement sending units hare flawed mechnisms...

Just my $0.02..