It's been a few years since I retired, so you might want to verify the following:
1) PCS mileage is paid for the transportation of you and any dependents. It is a flat rate. Makes no difference if you move 1 car, 2 cars, 1 car-1 truck and 1 tt - you get X cents per mile of the official distance between the two duty stations.
2) A partial DITY (Do It Yourself) move is set for a reimbursement based on rental of a commercial vehicle - U-Haul/ Penske, etc. It is also set by the weight moved.
There is no way I'd use my TT to move personal effects for a PCS move of over a couple hundred miles. Most TT only have a cargo capacity of maybe a thousand pounds, maybe 1,500. Frankly, you can move that better in your pickup truck than you could in the TT.
Also, you (and I and most folks) will be tempted to bulk out the TT - i.e. fill it to the maximum allowable volume with HHG/effects. That runs a serious risk of overloading the TT by weight. To the point that you will increase the likely hood of tire failure, frame damage, having the tow vehicle overloaded.
(Though if you have a toy hauler, you might actually have some good weight capacity.)
Yes, moving the TT at 9-10 mpg is going to eat up the mileage reimbursement for the PCS pretty quickly. So did moving a ski boat which many of us have done over the years.
Before you commit to using the TT to move personal effects - be sure to weigh it and the truck. Then calculate how much carrying capacity you have left.
I'm almost certain that it will be much less than you had planned.