Hey Justin,
The documentation on
https://community.marketo.com/MarketoArticle?id=kA050000000KzXJ&src=#5 is very handy in getting the necessary instructions to your IT team for SPF, DKIM, and CNAME setup. If you've already done this and received confirmation from your IT team that all have been completed, yet are still seeing performance issues, double check that you've submitted the follow up materials to Marketo support as well (Particularly item 6.7 for DKIM signing).
Marketo can't complete some of their setup tasks until your IT team has completed theirs, and certain tasks incomplete like the DKIM signing can have a big effect on your deliverability.
Hope this helps,
Jeff