i have this problem when i have less than half a tank of fuel.

when my orion was carb, it was steady as a rock, as soon as i switched to a "turbo tank" with a swirl pot i had exactly the same problems as you. i used the original carb sender aswell.

over half a tank and its steady, but if i'm under all i have to do is pull away from lights and its below the red when i glance down.