Why would a shallow well pump go on and off too much?
Your pressure tank is what is considered "water-logged". If it is a bladder tank, the bladder inside the tank may need to be re-pressurized or perhaps the bladder tank needs to be replaced. There is an air valve on top to do this, if it only needs re-pressurizing. 

To my recollection, and I may be wrong, and possibly your specs may differ, the tank, with no water in it, and the pump turned off, should have about 7 PSI of pressure in the bladder. You may need to drain the water lines in the house to do this. When the tank is then working with the system and the pump increases the pressure to 40 PSI+, then the pump should cycle as it used to.