An advanced active load-pull pulse profiling (ALPPP) system is presented to identify and track, for the first time, the optimum impedances along different sections of an RF pulse. Optimum impedance variations of a 10W GaN device within the RF pulse, and the resulting performance variations are quantified over an output power range of 25 dB showing a significant variation at power back-off. Furthermore, the nature of optimum load variations is probed through the addition of a pulsed IV capability. Pre-bias is utilized to investigate the impact of traps on device behavior over a range of temperature and drive power levels. It is demonstrated that pre-filling the traps provides for an almost constant load optimum across the RF pulse while maintaining device performance. Moreover, the identified optimum pre-bias condition, shows improved device linearity over the duration of the RF pulse, hence, suggesting a new method for compensating impedance mismatches and improving device linearity within an RF pulse.