The change over was between '04 and '05. both had the 6.0 PSD, so there must have been a change in the axles or frame.
a bit of reading form wikipedia:
Facelift (2005-2007)
Because
Ford Motor Company discovered that over 80% of the Super Duties were used for
towing heavy
trailers on a regular day-to-day basis,
[2] Ford restyled the line for 2005. Exterior styling was given a minor update with a new front end, however, this facelift has major strength improvements.
Major changes over the previous generation of Super Duties includes increased payload (
GVWR) and towing (
GCWR) capacities, a new taller front grille, new interior, standard locking
tailgate, 10-17% thicker partially boxed frame, higher amp
alternator, upgraded and larger 4-wheel
disc brakes (13.66-in front and 13.39 in (340 mm) rear rotors) with huge twin piston calipers, upgraded engines, upgraded automatic transmission option, an all new optional built-into-dash
Ford TowCommand TBC (
Trailer Brake Controller) that is fully integrated with the truck's PCM (
Powertrain Control Module) and ABS (
Anti-lock Braking System), an all new optional built-into-dash 4 AUX upfitter switches (for adding off road lights, winches, snow plows, etc.), and an optional drivers side glove compartment.
The two previous gas engines were upgraded from the old 2 valve per cylinder to 3 valve (2 intake and 1 exhaust) per cylinder. The standard 5.4 L V8 puts out 300 horsepower (220 kW) and 365 foot-pounds force (495 N·m) of torque, and the optional 6.8 L
V10 puts out 362 hp (270 kW) and 457 ft·lbf (620 N·m).
Ford's "Fail-Safe Cooling System" is unique. This system is designed to protect the engine due to loss of coolant (since these engines can not overheat for being 'overworked'). If the engine overheats, it will automatically switch from 8/10 cylinder (depending on V8 or V10 engine) operation to alternating 4/5 cylinder (depending on V8 or V10 engine) operation. Because there is now 50% less hot combustion, the engine will operate cooler. The vehicle will continue to operate, but with very limited engine power. The now so-called 'dead' cylinders also act like an air pump to cool the engine down even more. This system allows the driver to travel a short distance to obtain service or to reach a repair facility. The distance that can be traveled depends upon vehicle load, outside temperature, and current road conditions.
Only 2 transmissions were made available for the redesigned 2005-2007 models. The standard M6OD 6-speed manual overdrive and the optional heavy duty
TorqShift 5R110W 5-speed automatic overdrive with Tow/Haul mode which replaced the 4-speed 4R100 used in the first generation.
Ford offers a PTO (
power take-off) which provides direct engine power for accessory equipment without the expense and installation time of separate, independently mounted electric motors or other power sources. The standard equipment 6-speed manual transmission comes with an integrated PTO. The optional TorqShift 5-speed automatic transmission can be equipped with an integrated PTO provision (it automatically locks the
torque converter providing power to the PTO gear when the operator turns on the PTO switch).
On 8' long bed models the fuel tank capacity is 38 gallons and the 6.75' short bed models are 29 gallons. Depending on models the optional trailer
tow hitch receiver comes with a 2" or 2.5" Class V receiver and 4- and/or 7-pin wiring harness in either 12,500 or 15,000 lb (6,800 kg). All Super Duties come with a Towing Package standard that includes an external oil and transmission coolers installed regardless if the factory hitch receiver was ordered or not. Depending on model and options, the empty title
curb weight is 6,000-8,000 lb.
Approximate
payload capacities are 3,000 lb (1,400 kg) for the F-250 Super Duty, 4,000 lb (1,800 kg) for the F-350 Super Duty with Single Rear Wheels (SRW), and 5,800 lb (2,600 kg) for the F-350 Super Duty with Dual Rear Wheels (DRW). This generation of Super Duties has exactly double the payload capacity as compared to the older traditional (non-Super Duty) F-250 and F-350 trucks. By direct American comparison to the F-250 SD the
Chevrolet Silverado 2500HD/GMC Sierra 2500HD is rated at 2,600 lb (1,200 kg) max and the Dodge Ram 2500 Heavy Duty is rated at only 2,100 lb (950 kg) max payload capacity.
Approximate
towing capacity for the F-350 Super Duty is 19,200 lb (8,700 kg) max. By direct American comparison Dodge Ram 3500 Heavy Duty is rated at 16,400 lb (7,400 kg) max and Chevrolet Silverado/GMC Sierra 3500HD is at 16,500 lb (7,500 kg) max.
