The SD V10 is a towing machine, but it does have the aerodynamics of a BIG chipped brick... with fuel economy to match! But it should be pretty close to your old 150 when towing at the same speeds. Please come on down to the V10 fourm to find out all you want to know! Don't be afraid to let the V10 rev when working it. It makes its best towing power from 3500 up.

We tow a Nash 22H, usually with toys as well (quads and or motorcycles in bed and on racks). With 4x4 chassis and big tires, we usually get 7-10 mpg while towing at around 60 mph. Wind and mountains lead to lower numbers.
2WD and smaller tires will get some mpg back.
Speed affects mpg dramatically when towing a full frontal area tt. At 70-75 mph with some headwind, I got it down to 5.....