Do you have a custom return-path configured? Using a custom return path might help, because it ties your reputation primarily to your domain.

ESPs check multiple factors. Both IP and domain reputation play a role. They will check your return path / envelope sender domain reputation and your IP. Your domain will start with it's own reputation, but can be boosted with a good IP reputation. But if your domain had bad sending behaviour in the past, that might be an issue.

Source: I'm running a transactional mail service that solely works with shared IPs: https://www.markix.com.