Things to watch for when buying used?
 

Howdy, I've been looking to upgrade from my old Powerstroke. I had been looking to either go to a Duramax or a Dodge 5.9, but I found a 6.7 that other than being an automatic (and yes I was willing to get an auto trans in the Duramax, because they seem to have few problems and Duramax sticks are rarer than hens teeth) is just about the truck I am looking for. 3500, long box, quad-cab, bare bones base model with vinyl floor (I would pay extra for this, over carpet, but luckily for me, it is standard on the cheaper models) it even has roll up windows and manual door locks. :). The body is dinged up, but that isn't a big deal to me, since it will be a work truck, and most of the dings are in the bed and I intend to put a flatbed on it, anyways. It is bone stock, with 137K on it, and just had the tie rods replaced.
Thing is, I know nothing about the 6.7's, so I've heard the auto tranny in them (this is an 08, did they put different tranny's in different years?) is much tougher and doesn't have the problems the 5.9's and the Fords have always had with autos on diesels. Is this true?
Also, what else should I be looking for, potential issues, clues to abuse, etc.? I mean I know it was a company work truck, and obviously from the body the employees didn't treat it with kid gloves, but I'm concerned with non-cosmetic issues, or anything cosmetic that might indicate potential non-cosmetic issues.

In 07.5 the started to use a 6 speed automatic called the 68RFE. These transmissions in stock form are typically reliable in stock form compared to the older year transmissions.

The down fall when these transmissions need to be replaced they are typically big dollar compared to a 5.9 transmission or the Allison out of a Duramax.

find out if the exhaust brake works (little button under HVAC controls). if not, it could be indicative of abuse and replacement VGTs aren't cheap.

ask if you've got any warranty or rescission period at all - if the DPF or EGR is plugged, that's $$$$ to get unplugged. or time - your time - to unplug it / clean it out / replace stuff as applicable. if you plan to delete it immediately, obviously that's not as big a concern.

i'd plug in a scan tool and pull codes at very least. also, a vehicle history report should indicate that any recalls which have been announced have been taken care of.

if the seller is amenable, you could jack the front end up a bit and check the ball joints, since chrysler is famous for weak ball joints that fail way before they probably should. then there's the super-scientific sniff tests: fuel smell on the oil dipstick could mean excessive blowby. if you smell fuel in the oil dipstick, put it back and loosen the oil cap to the point it just sits over the fill hole. if it dances, there's a problem. if you can see smoke coming out of the dipstick tube or the fill hole when the engine is running, there's a problem. trans fluid should not smell the least bit burnt, because as Motorops pointed out, when these 68RFEs go, they tend to take big chunks of your disposable income with them.

if it's 4x4, check that you can shift-on-the-fly up to about 40 without any grinding noise. is that a good idea to do? not really, but the manual says you should be able to engage 4x4 "at reasonable highway speed" which to me means 55 but no reason to push it in case the seller ascribes to the "you break it, you bought it" thing.

as with any truck, maintenance records are good. the more the merrier. check engine hours, divide total miles driven, and that'll give you average mph - this is an indication of idle time. cummins recommends, just as ford and GM do, different maintenance intervals for high idle time (severe or extreme duty schedule), so if the records and idle time don't jive... not that it's a no-go, but something to be aware of.

i'd probably also check the u-joints for unwanted play. you know all those high-mileage niggles (for gassers) to look for... buddy of mine summed modern diesels best: half-million-mile engines, wrapped in 100k trucks.

best of luck with it, and welcome to the Indiana Inline family!