Actually, my truck is in at the dealership today getting the 48-gallon Titan replacement tank installed as well as replacing my fuel filters because I have ~290 Engine Hours and with biodiesel it is recommended to replace fuel filters every 300 Engine Hours. They should have my truck back to me tomorrow. I already reprogrammed the truck to have the 48-gallon tank size via FORScan before I took it in to them this morning.
All F150 diesels are standard with the 26-gallon tank size, and you need to have the 6.5' long bed in order to get the 48-gallon Titan replacement tank. If you do, and crawl under your truck you will see a big open area in front of the current fuel tank that allows for the jump up in tank size. I'm not sure why Ford didn't offer tank size options up front for the 6.5' long bed either--but it can be done via aftermarket.
My average mpg over the last 1,243.7 miles is 25.9 (lots of interstate highway miles in there, I was at 28.3 until doing a bunch of around town driving). 25 mpg * 48 gallons = 1,200 miles on a tank. I'm looking forward to not fueling up as often.
I will post an update on this in the Titan Tank thread with some more information within the next few days to week.