My 5.9 24v is DEF-free; 2001 didn't have any emissions. Love it. Smells like a diesel is supposed to smell! But that said...I'm not going to mess with my Eco. It works great the way it is. It's not "fast", and that's OK. If I need "fast" I get on my 370 lb motorcycle with 152hp at the rear tire. The Jeep isn't a tow monster. If I need to pull the enclosed car trailer...I grab the keys to the Cummins. It IS a fuel-efficient, luxurious, extremely capable 4x4 SUV that I think is actually very attractive. It's easy to drive, and it's dead-nuts reliable...so I'm not poking it with a stick.