I am trying to set a ship date automatically when a sales order is first loaded. I have my state to set the field to ten days from now on record entry. It works for about a second, then gets reset back to todays date. How can I get my WF to stick?

It sounds like your workflow is restarting after it leaves the last state. Can you check the do not exit workflow box?

Is that logic applicable to all sales orders? If so, i think there's a preference in Setup > Accounting > Shipping or somewhere where you can put x number of days to define the expected ship date