There is a vent on the top of the tank that looks like this:
It will next to the sending unit:
Odds are the vent is either shot or stuck closed. If you can get at it and pull it out shake it…it should click when you shake it like a bottle of whiteout.
My guess is that vent needs to be replaced or cleaned. When you drop a tank you can disturb crap in the vent line that will plug the vent from the top.