A solution to the cheapest cost considering all of your options might be :
Change your tires to a larger diameter highway tire .
The odometer will turn over less miles and the rolling resistance of a highway tire ( especially these new fuel saver types ) will help you pick up real fuel mileage in actual usage .
Your diesel has enough low end torque and first gear is plenty low enough to handle this .
Further the tires themselves will go a greater distance .
You only would have to insure one car and maintain one car and polish one car and park one car ( inside i hope ) .
Two of my RV buddies have high mileage Powerstrokes one with 300,000 the other with 214,000 on the odometer .
Drive that fancy smancy H-D pickup and take care of it .
