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Originally Posted by rustyk
Well, I get about 9.3 mpg, but then my 6.5L TD is in an 18,000 lb. class A motorhome.

Things do change - with my replacement Peninsular Diesel AMG 230 HP (custom spec'ed) 6.5L TD, mileage is nearly 11 mpg...
Do a little here, do a little there...with the Suncoast HD tranny and TC, redoing the diffy (Someone had been in there previously and the pinion bearing clearance was way tight), and fixing a stuck caliper, consumption is now averaging 12.2 mpg over the last 5K miles.