How Many Miles Before Towing with New Ram 3500

I agree with others on the rear diff gears needing break-in. There are two break-in periods. First while not towing, second while towing.

Copy and Paste from 2014 Ram Owner's Manual on page 601 under "Towing Requirements":

CAUTION!
• Do not tow a trailer at all during the first 500 miles
(805 km) the new vehicle is driven. The engine, axle
or other parts could be damaged.
• Then, during the first 500 miles (805 km) that a
trailer is towed, do not drive over 50 mph (80 km/h)
and do not make starts at full throttle. This helps
the engine and other parts of the vehicle wear in at
the heavier loads.

Randy's Ring and Pinion has an explanation of why. clicky

Enjoy the new truck!