What is the difference between present day factory rated torque figures in the fancy dealer brochures and the torque at the back wheels on a dynometer?

This past weekend a friend had a Predator upgrade chip installed in his 2003 Dodge diesel. It is factory rated at 550 ft lbs and it was dyno'ed before and after the chip was installed. Before it was installed it had around 750 ft lbs and after it was installed it had 937 ft lbs of torque. The dyno result was taken in 5th gear which is direct in the Dodge 6 speed transmission.

Why would the factory rate it at 550 if it is indeed 750 at the rear wheels?

I thought it would be less at the rear wheels.

It sure did pull with the chip installed. We were towing a tandem axle car trailer with a 94 Pontiac Sunbird on the trailer. We weighed 14,000 lbs at a scale and this thing drove down the highway at 70 mph and passed like there was no tomorrow.

Blaine Dumkee
59 GMC 9314
Fort Smith NT
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