This work describes a new power amplifier, PA, behavioral model intended to predict both the PA amplitude and phase input-output signal relationship and the average or instantaneous dc power consumption and thus average or instantaneous signal-dependent efficiency. Hence, contrary to other previously published PA behavioral models, such a model is not only capable of describing the complex low-pass equivalent fundamental zone output, but also the real low-pass current consumption output. In addition, a special attention is paid to accurately account for the multiple time-scale dynamics shown by modern GaN HEMT based high power amplifiers.