Voltage output KW FX801

2009 or 2010 Lazer Z kw fx801-aso4 Just put on new voltage regulator. With pto off puts out 13.8 to 14.1 volots when pto is engaged and blades are on voltage out put drops to 13.0 to 13.1 is this normal? I would think voltage out put would be close to same. What could cause the drop in voltage. All the readings are at full throttle.

Thanks Bob