Something is stuck in that position. I would fill it up and drive it on a winding road, with lots of break check and see if that loosen it. If not you will have to take it apart and manually reinstall it gently. You don't have to drop the thank to get to the unit. Just lift the bed high enough to get your head into it...
Probably the float arm got bent down when wrestling the old float off the SS arm (removed float) or the arm got bent during install, or someone purchased the sending unit & monkey'd with it, then returned it when realized it was not the problem