Daniel,You need to describe very precisely what happens. For example, why do you think the pressure switch shuts off? How do you know the pressure gets to 80-90 psi? As previously noted, if the well is off, it is impossible for pressure to build further, so possibly you are being fooled into thinking the pressure switch is off, when it is still calling for the pump to run.
I don't belive the pump will go to 80-90lbs psi you didn't say what HP the pump is, i have 1 1/2 HP pump and i turn on the bleed down spicket in a hose to run out side the pump will pump up like 65 or so pond's of preasure that is the most that pump will do . I belive i would get another gage , they make one that goes on to a spicket turn that on and have some one watch that one i bet it doesn't go 80-90lbs psi which is should do if that is the water preasure.after pressure switch shuts off at 50lbs the pressure continues to go up to 80-90lbs psi, what is the problem