I had a 2008 a non DEF Ram CTD and I had 24,000 trouble free miles but the fuel mileage was horrid. 3.73 gearing 12-13mpg highway/ 8-10mpg towing
Fast forward to today I have a 2014 DEF Ram CTD and I see much better fuel mileage. 3.42 gearing 18mpg highway or better 12-14 mpg towing. and it's not broken in yet.
I really like the DEF model much better. It sounds more normal and the turbo seems to be more free. The Non DEF model seemed like the timing was way retarded and just didn't sound right as you could rarely hear the turbo.