One thing that really helps beyond just the chunking approach is understanding the emotional arc and logic of what your character is saying - basically, why they're saying each line and what they want from the audience. Once you grasp the throughline of the monologue instead of treating it as random words, your brain naturally holds onto it better because it's following a story rather than memorizing disconnected sentences. Pairing this with physicality - adding gestures or movement to specific lines - gives your muscle memory something to anchor to as well, which tends to make the whole thing stick around longer.