We have a Thor Siesta 24SS. Also has the Mercedes Sprinter 3500 chassis with the 3L turbo diesel. We tow our 2 door wrangler...it weighs in at just under 5,000. We are a bit over combined GVWR, but take it easy.
The vehicle has enough power and with the braking shared between the Mercedes and the Jeep (via the ReadyBrake system of the toad setup) I don't feel any issues with braking. The tranny temps do rise quicker on mountain inclines with the toad compared to no toad, but I take it slow and easy monitoring the temps (using ScanGauge to monitor). Towing on flat highways the rig is great with the Jeep in tow.