Do you have access to e-Benefits? If so, are you a premium member? If those answers are yes, a quick way to check this requires logging in to the e-Benefits system and clicking on the Service Members Personnel Information link. Once the new window opens, click the tab for DAV, and you will find the info you seek.
This will answer your question about the P&T modifier. However, I suggest contacting the DAV, AMVETS, VFW, or VSO to get a more directed answer regarding the IU question.