Found this, and in my experience, if your Travel Card people have never been asked about this, you might wanna hand them this if they look at you like you are crazy....PCS program guidance
And it is in the DoDFMR (Department of Defense Financial Management Regulation) Volume 9 Ch. 3, and states:
The Department of Defense (DoD) policy is that the Government Travel Charge Card (GTCC) will be used by all DoD personnel to pay for all costs related to official Government travel. Official government travel is defined as travel under competent orders while performing duties pertaining to official government assignments such as temporary duty (TDY) and permanent change of station (PCS) (where applicable).