Ford installed diesels in the E series from 1982 until the end of the 2007 model. The introduction of the 6.4L to replace the 6.0L made if unfeasible to install the new engine in the chassis.
Chevy/GMC installed the Duramax in the Savannah from the 2006 models thru the 2016 models. I suspect it was discontinued due to lack of demand. The few I have seen were panel models, not full window bus models, but I am sure there are some out there.
The Sprinter thru the 2006 models has a 3500 lb tow rating with the I5 diesel and the 2007 and up models has a 5000 lb tow rating. I have seen a Sprinter panel model towing a 24 footish sized travel trailer in a campground.
The Transit models have a 3500 lb towing limit also.
Charles