Get a decent, accurate pressure guage to check the pressures rather than relying on the guage on the compressor.
Had some one complaining of a firm ride in their family saloon - pressures he assured me were fine as he had checked and inflated them to the correct pressures with his new plug in compressor (therein was the clue).
They should have been 36 - 38psi when put on the calibrated guage they were actually at 57 psi :-o