Are you pushing the pump handle to the bottom of it's stroke or just stopping when the compressed air in the pumps piston starts fighting back? I don't know about your pump, but pumps that push more volume of air per stroke will get quite difficult to push the handle down that last 1/4" they need to go.
If you suspect the gauge in error, then go get a hand held gauge that will fit your valve stem and check if it shows a big difference from what the pump gauge shows.