I have installed a 3 aftermarket fuel & sending unit gauges. I seen to have a difficult time having them read correctly at the ends of the sweep (either full, or empty).
Seems one end is always off a bit, one didn't read full when the tank is full, and one didn't read empty when it run out of gas. I even had one that didn't read full when full, and still showed fuel when it ran out, but the other two were off at one end or the other. In that case, its better for it to not read full. Walking sucks when you think you still have fuel left.

Might just be me, and I'm not sure what caused the gauges to read like they did, but since I'm 3 for 3, I have to admit it must be installer error. For the record, I followed the directions, the last one I even double checked. That's my experience. Gene