As a general rule, is 99mg of potassium once daily enough to correct a deficiency level of 3.2? and can this level cause shortness of breath?

As a general Rule: As a general rule it is much better to find the cause of the low potassium and to correct the cause rather than just give you potassium replacement.

More potassium: I recommend that individuals with a low potassium take supplements and eat potassium-rich foods several times per day. Take the supplements with your meals which helps with the absorption. Also increase foods with higher potassium in your diet such as bananas, orange juice, sweet potatoes, regular potatoes and cashews. The low potassium itself does not cause shortness of breath but weakness.