I am Loreen Ozolins. I am a Senior Certified Chi Running Instructor.
Thanks for your question.
If you are 5’3” – 5’10”, then yes, you are correct that the optimal cadence is 180/min.
There are a couple of suggestions on how to maintain your cadence.
One suggestion to help retain your cadence, regardless of the speed you are running is to take more advantage of your pelvic rotation. By rotating your pelvis, particularly at higher speeds, you can take more advantage of the “hang time” in your longer stride length, in order to keep to the 180 cadence.
Another suggestion is to run with a metronome if you do not already do so. A metronome, even if beeping in the background without you consciously thinking about it, can assist your ability to keep to a steady pace.
The last suggestion would be to start to use your arms to keep pace with the metronome, rather than your legs. If you can keep a steady 180 cadence with your arms, your legs will follow. Let me know if any or all of the suggestions above works!