Dodge Repair Questions? Ask a Mechanic for Answers ASAP
The vehicle is not supposed to be driven with the OD engaged when a heavy load is being carried or towed - as indicated on the Owner's Manual.
If you were driving with the OD on, what probably happened is that the onboard computer noticed what was happening and shut it off for you so nothing would overheat and fail. Shifting the tranny to a lower gear should take care of the issue until the weight is off.