7,700 lbs according to L/R with coupled brakes, but I have done a couple of long distance tows with that or maybe more and no ill effects.
Depends on having adequate brakes on the trailer and not doing anything stupid.
Towed other disco's locally, a series one 107 station wagon from Pennsylvania to Houston and a 25 ft cargo trailer packed full of furniture from Boston down to Houston. Also my wife / daughter regularly tow a double horse box with large horses in and around Texas with one of the D2's.
The vehicle will manage it no problem provided its been well maintained.
Get a decent brake controller, make sure trailer brakes are working and bearings are good and you will not have a problem.
Simon