F-250s don't come with 3:55 gears.
Rear Axle Ratios
4.10 Axle Ratio $50.00
3.73 Axle Ratio
3.73 Axle Ratio, Limited Slip Rear $300.00
4.10 Axle Ratio, Limited Slip Rear $300.00
4.30 Axle Ratio, Limited Slip Rear $350.00
This is from the Ford website.
EDIT: But...the E-350 did, but they don't make an E-250.
Rear Axle Ratios
3.55 Axle Ratio
3.55 Axle Ratio (E-350)
3.73 Axle Ratio (E-350 Standard Length)
3.73 Axle Ratio
4.10 Axle Ratio $45.00
3.55 Axle Ratio, Limited Slip $270.00
3.55 Axle Ratio, Limited Slip (E-350) $270.00
3.73 Axle Ratio, Limited Slip (E-350 Standard Length) $270.00
3.73 Axle Ratio, Limited Slip $270.00
4.10 Axle Ratio, Limited Slip