Just turned over to 33k miles on my 2003 FX45.
Highway mpg:
Empty just me driving at about 65 mph, I average about 22 mpg on hwy. Recently took an 1800 mile round trip with 3 people and luggage often times cruising at 95 mph and then I was getting 18 mpg.
City mpg:
Looks to be around 12.5 mpg. This kinda' sucks.
On a positive note, the cruising at 95 mph was the smoothest and quietest experience I've yet had at higher speeds in any vehicle. Around town, I'm very impressed with the transmission gear shifting program. I think much of the FX45's pizazz or perception for power/torque is due to a finely tuning transmission.