Fuel needle fluctuates while car is in movement

Buick Century 1987 - 2.8L
Sending unit measures: Empty 9 ohm - Full 88 ohm
Fuel pump working while engine is running or key switch in ON position (working properly).

Issue: Fuel needle fluctuates while car is in movement and the engine stops when the car is going downhill and suddenly is braked (half tank), Is normal this behaviour in this car? Is this car equipped with a 'anti-slosh module'? if yes, where it is located? Possible solutions?

Thanks in advance!

I doubt that this year vehicle had a built in "buffer" circuit.....however, with it being almost 27 years old, that fuel tank could have bee replaced, and if it doesn't have a baffle in it, to keep the float from moving all over the place, when going around corners, sudden stops and accelerations, etc., that could be the problem....