The Cummins 6.7L is the old ISB 5.9L upgraded a bit. By all reports it's every bit as fine as its predecessor. I believe its rated at 750 lb-ft of torque and 350 Hp in the RV application. Whether that is "enough" depends on the weight & size of the coach - the RV industry rule of thumb is that a coach needs 1 hp for every 100 lbs of coach weight. That says the 6.7L should move a 34,000 lb rig around ok. Given that a '08 Discovery has a GVWR of 31l lbs, it ought to be fine. That 1:100 rule of thumb is perhaps a little wimpy for steeper grades, say over 3%, but it gets you to the top. More Hp gives peppier response and faster hill climbing speeds.
Back in 2008 the Discovery was Fleetwoods mid-range DP, more upscale than the Bounder or Expedition diesel but not quite in the Excursion/Providence range and well short of the American Coach luxury models. That said, most Discovery owners find them quite pleasing in amenities and as good as any in its price range.
A 2008 will be built on a 2007 or 2008 Freightliner Custom Chassis and thus adheres to 2007 EPA engine rules. Those rules caused a loss of mpg vs 2006 and earlier models.
View the 2008 Discovery sales brochure at https://big.nyc3.cdn.digitaloceanspa...20190801124528