Mutual coupling effect on three-way Doherty power amplifier is studied, where the amplifier is targeting 3.4-3.8 GHz for 5G applications using three GaN HEMT transistors (6W, 25W and 45W) to achieve a 76W peak power. A new impedance modulation configuration is used, where a gain of 12. 5dB was achieved over the design band. Changing the location of the peaking amplifier or changing the operation sequence of the peaking amplifier can achieve good efficiency at the back-off region. In addition, the performance variation of the designed amplifier was tested for different Voltage Standing Wave Ratio (VSWRs) considering the antenna impedance changing due to mutual coupling. There was an average of 3dBm output power variation and \pm 1y% efficiency variation at the peaking power and fewer variations in the performance for both factors at the back-off region for different VSWRs.