Intellitronix Fuel Gauge Reverse

First, try to contact Intellitronix.
To me it sounds like you've got something hooked up backward.
Our sending units are 5-8 ohms full and 60-75 ohms empty.
Other brands can read opposite. A Jeep Cherokee, for instance, reads 0 ohms empty and 90 ohms full.
Stands to reason that their electronics are capable of reading either, just with a different hookup or setting.
As I said, call them.