As the pressure increases on a submersible pump, the amps will decrease.This is normal.
The symptoms you describe almost sounds like a hole in the drop pipe.
A hole will make the pump work harder trying to fill the tank, and will take longer and longer to fill the tank.
Are you getting more air than normal?
If the is a relief valve or a plug in the top of the well that can be removed.
Take it out after the pump shuts off, and if the water drops real fast, you more that likely have a hole in the drop pipe.