Josh,

Typically, you are authorized travel time, mileage, and per-diem from your home of record.  However, because of your TDY, you may not receive the travel time, but, you should still receive at least the mileage and per diem.  It’s best to check with the transportation office where you are to confirm.  In the meantime, here is a link that might help answer some of your questions, specifically #9 “Per Diem for PCS Travel.”  http://www.defensetravel.dod.mil/site/faqpcs.cfm

I hope this helps.