We have just done the same thing. From a Ram diesel dually and a giant 5th wheel we went down to a 2010 3500 Chevy Express 15 passenger van and a 2015 Puma 30RKSS. The van was necessary to haul all of the "stuff" that fit in the underbelly of the 5er but not in the TT. We removed some of the seats and may remove one more row.
The 6.0 Vortec engine does just fine pulling the 8800 pound GVWR TT.
I did find a low mileage Ram 1500 with the diesel but found that the specs were too light for towing our TT.
Storage will be an issue so a truck cap will be needed if you go with a pick up. The fridge will be smaller and you can forget that big closet in the nose of the 5er.
We found several "almost" trailers in our search in your price range so they are out there.
Good luck with all of it
