2003 Ram 3500 5.9L Cummins. 121,800-something miles - completely stock. Turbo replaced almost 2 years ago after it seized - no further issues whatsoever.
I tow with it weekly, heavy 4 horse trailer with small living quarters. Usually 80 to 140 miles round trip a day - once maybe twice a week. Fuel and air filter changed at 116-117kish (know this because it's about due for a change) when I did the oil change.
Filled up last Tuesday or Wednesday in town 20 miles away. Truck ran "ok", ran errands etc vehicle wasn't loaded, then out 40 miles and home with the trailer Thursday - fuel economy being a little less than what I usually get (was 14, usually roll high 15-16 mpg - by hand calculation matches trucks calculation on the liar). Next day, Friday, ran it to town with the trailer still on, 40 miles round trip. Friday evening ran it 140 miles round trip (1 horse and equipment - old steel trailer that's probably 6k empty - so with horse and equipment and crap, 8k) and that's where the trouble started on the way back. Sluggish to shift on the way home, wanted to stay in the lower gears even warm, even hand shifting off stop signs and such into 2nd it didn't want to shift up until late, sucked about half a tank of fuel in that trip - no hills to speak of (live in OK) and speeds around 55 for most of it.
No codes thrown, DTE said 0 miles 25 miles from home, drove it all the way home because I had to and no fuel stations between point A and B I can get into with a 32 ft trailer, unloaded the trailer, parkedi t for a day, then drove down to put fuel in at the place close to my house. Driving down to the station same thing without the trailer, sluggish to shift 2.5-3k RPM before second and third gears. Put 7 gallons in it, drove home like a champ without dragging to shift or anything. Normally half a tank is more than enough to get me there and back with plenty of room to spare because I know there aren't any filling stations I can get in and out of reasonably along the way.
Not the trailer either, I thought maybe I had a brake locked up that was dragging and causing resistance, but tires aren't showing any wear and everything seems functional, bearings greased this spring.

So, just get some not so quality diesel? Seems like it resolved but I haven't driven far since, but planning on the same trip again on Friday with the same load and don't need issues along the way as I have no way to haul my trailer home if my truck bites the dust, our other 5.9 doesn't have the gooseneck installed yet.
Anything worth checking out before I run it Friday?

 

See if your water separator found anything.

As for the station you fueled up at before all the trouble started, have you gotten fuel there before?

 

It sure sounds like some bad fuel. Especially when once it was gone, the problem cleared up. I'd check the separator and filters for crud. Quite possibly you either got fuel at a station that doesn't sell much diesel or it had just got a delivery and all the garbage in the bottom got stirred up. We had a local station that had gasoline put into the diesel tank. Major problems for a bunch of customers.

 

No, I've never gotten diesel there before, it was just convenient while I was in town. I live about 20 miles from town and we only have the smaller gas stations, one of which you can't use a debit card at after hours, but they have high turn overs on diesel because of all the farm trucks.
I guess I would have expected the WIF light to come on if I had water, but from what I read that doesn't always happen.
Not sure if the fuel filter will be obvious, I ran it almost bone dry because I didn't have a choice, I fully expected to run out and have to get someone to bring me a can and prime it to be honest. I wouldn't have done that had I known it was going to drain out 15+ gallons in 140 miles! Guess I can drain the canister into a jar and let it sit and see if it separates.

Truck ran fine today.

 

Definitely bad fuel. You may have gotten lucky on this one.

 

Maybe, I don't usually get lucky. Tomorrow will tell though. Almost tempted to finish the floor on my bumper pull in case it does decide to act up so we can at least get the trailer and horse home - but I can phone a friend with a gooseneck ball if need be I suppose. This truck has never ran doggy at all, so color me shocked when it acted like my previous Ford diesel lol.

 

I've run 2 tanks through it since then, must have been crappy diesel because it has run perfectly, loaded and unloaded well over 800 miles since without a skip. Thanks for the help, I didn't want to bomb my truck because I missed something that could be causing it other than just got a bad tank of fuel.

 

You might mention this to other oil burner owners. Furd and Chebbie too so they know about that station. We have a local station that put diesel and gasoline together in the same tank and spent some big bucks fixing the problems it caused.