Testing the sending unit versus the gauge was going to be a pain. I ordered a sending unit. It fixed the problem. I have not filled it or driven to empty to check accuracy. But looking at the amount of gas in the tank, it seemd to read right. Andd after adding 5 gallons, it seemd to go up the appropriate amount.
Therefore, short of a computer to check codes, my guess is that if you measure 12 v on supply and 7v middle pin when unplugging the connection to the sending unit. The problem is probably the sending unit.