WARNING: This page is about a different car, the 2004 Ford RV Cutaway, 2004 Ford Econoline, 2004 Ford E450 Super Duty, and 2004 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Transmission Code
Courtesy of FORD MOTOR CO.
5 - Four-speed automatic overdrive (4R75W)
B - Five-speed automatic overdrive (5R110/Hi-Torque), diesel