First if you only have a 3/8 line going to the machine I would try bumping it up to 1/2inch or 3/4. One way you can check this is to look at the incoming air pressure gauge or regulator. If the pressure drops at all while machining you probably have an undersized air line feeding it and/or at the firthest point from the compressor. When does it generally occur? during tool change? spindle airblow? When an operator blows off his part? palletchange or some other operation?