Besides major leaks or premature bleeding, you may want to check:
(1) intake filter, if this filter is too dirty the inlet pressure will drop to make the outlet pressure also drop
(2) control panel, anyone tampered with the max pressure setting?
(3) if it is a water-cooled, check water level, too hot a cylinder head will cause a lower compression ratio
(4) if you newly installed it, double check that you did not mistakenly wire up a wye instead of a delta to get the right HP and RPM for the 3 phase motor given your local 3 phase voltage. And that you did not wire it up to rotate in the wrong direction which may cause the lubricant to run dry and thus raising the head temperature