u might wanna PM some of the guys earlier in this thread that have been driving then awhile
(minnie, dpan, or the pill)
these are good trucks.
but your question will no doubt attract the anti-oval crowd.
keep in mind the 6.4 is really a continuation of the 6.0...
but with many modifications leading to the newer version.
this was also the FIRST of the units with DPF and REgeneration.
my 6.4 is doing fine and the 6.0 before that did great towing too.
plenty of power, quiet, clean and easier to service than the 6.0
NO DEF (urea) so maintenance cost is a bit less than the new 6.7
the MAIN issue with the 6.4 if fuel economy.
IF u can keep yer foot out of the turbo/boost the mpg will be better,
but it will still be 2-3 mpg LESS than the new/6.7 and less than a 6.0
with lots of commuter miles the DEF/REgeneration should happen less often
than a truck which idles a bunch or puts around town.
so ONE thing to check is the engine hours vs miles
IF the truck has a LOT of hours but lower mileage it will take a bit of driving to clean it out.
when REgeneration is happening mpg goes down because EXTRA fuel is used in the heat/burn/clean process.
the tranny is very good, brakes are very good and the body, interior and electronics good.
i like the ride quality and it's much smoother than the 99-07 250s.
the built in brake controller, mirrors, tow/haul and other TOW READY features are great.
my suggestion is keep it over night for an extended test
and find a LEAST one other used 6.4 for comparison test drives ...
along with the recalls, the dealer should be able to print out ALL of the dealer service history.
while the coolant is good for 100k, i would ask 4 a coolant flush, tranny service, rear diff change and fresh oil.
fresh lubricants are essential and they will never be less expensive than right now at dealer costs.
NEW TIRES is another request item.
one can tell a lot by looking INSIDE the engine bay, it should not be dirty, oily or mucked up.
nothing wrong with a truck that's been used and seen hard work,
but dirty, smelly or subtle signs of abuse should be avoided.
at ~50k miles it's just broken in.
don't forget the pictures!