Price list syncs are taking a very long time, over 20 hours. Not to mention it usually errors out and needs to be manually restarted in this time period.

I have tested this with a lot of price changes, and minimal price changes, and the time to sync did not change.

Is there a better way to automate this process, and to only update the items which prices have changed (either + or - amount)?

BigCommerce did recommend using Price List Importer/Exporter | BigCommerce. I have tested this on Sandbox, and this is a very fast way to update multiple price lists for multiple items at once (I did about 6,000 items in < 10 seconds). While this is an adequate solution, I don't see any way to automate this.