So,I decided to try this
Hey, try anything once! Sometimes two or three times.
I had the same issue with my fuel gauge in my 66 barracuda. I used the 7805 5v regulator. Yeah, I know, I used all red wire...it's what I had.
Once I got the voltage regulator working, my gauge would read 5/8 when full. Sending unit measured correct resistance out of the car.
I did it about a year and half ago, but just the other day I filled up and the gauge went to 7/8!
I should add that a couple of FABO members guided me through the repair: Pete_in_NH and nm9stheham. Thanks!
Here's a picture of my repair.