After checking all wiring, moving the ground and checking the sender output with no resolution, I decided to start with the sender. Bought a new sending unit, veified the Ohms output prior and installed it this past Saturday. All is good, fuel gauge reads appropriately.

Oddly, the sending unit I took out was putting out 72 Ohms which should have caused the gauge to read 3/4 of a tank, however it read below Empty. I would guess there was more to the issue than the Ohms reading.

I appreciated everyone's input on the problem. Unfortunately the tank does not lend itself to the "stick" method of checking fuel level. The boat also does not have an hour meter, so tracking by hours run is not practical at this point.