Which of the following would cause your FM transmission audio to drop out on voice peaks?
Why FM voice channels are limited to about 5 kHz deviation to fit the receiver's IF passband. Shouting into the mic drives deviation past that limit, so on loud syllables the signal splatters outside the receiver's filter and the audio breaks up or drops out. The cure is to back off from the microphone and speak in a normal, steady voice.
Watch out Too little deviation does the opposite: the recovered audio is weak and quiet all the time, not chopped up only on the loud peaks. Repeater offset errors and high power don't distort voice peaks at all.
Dropouts only on the loud parts = overdeviation. Back off the mic, don't shout.