I have a 2015 780 and run wis to ca and I have the Volvo d13 with the xe package it has the a single drive axle with a tag behind( would I do this combo again probably not a single axle or the 455 hp settings.) as for the truck overall I am happy gets great mpg I ull a refer so if you a have any questions ask, I've had the truck for just under a year I will give you the honest answers to your questions!
weight numbers seem to be on the high side to me, I can haul 44500 if I watch my fuel levels and that is with a 780 and a refer so you should be good with the 670 in my opinion.