The air pressure in the pressure tank should be 2 pounds less than the cut in pressure of the pump . The air pressure in the pressure tank must be checked with the pressure tank drained of water . Your statement that the cut on / off pressure is 35/45 is a little confusing . There should be 20 pounds difference between cut in & cut off . You are correct that with 38 pounds air pressure in tank the pump should cut on at 40 & off at 60 . Sounds like your pressure switch needs adjusted .