Whirlpool washer

I'm assuming you have a top load Whirlpool washer with buttons and knobs, instead of electronic controls.
There are some things that will cause a washer to overfill. The only one that will cause it to underfill is the pressure switch (water level switch.)
Some older machines (15 yrs+) have a ***** on the back of the pressure switch to adjust for the fullest load. If that ***** has moved, that would explain the lower levels. If the pressure switch is plastic (nearly all newer models,) the switch is not adjustable and should be replaced.