Over the past week or so, I've had to make numerous trips between my sister's house in Sacramento and Oregon, then down to SoCal and back to Sac to move some of her things into storage as she passed away recently. During the last trip to Oregon, my truck began to sputter going up even the slightest incline, no matter how fast/slow I was going (although I really haven't noticed it below about 45 mph). If I stomp on the gas, it stops sputtering, but if I'm in traffic, I can't always stomp on it (even though I'd like to!). It seems to run and accelerate fine when its a little cool, but the sputtering begins after about an hour or so into the road trip. I left SoCal around 11 AM and sputtering became noticeable around 2 PM after constant driving at around 70 mph.

First inclination was to replace the fuel filter, which I did last week. Had the oil changed last week, as well. When I got to Sac 2 days ago from SoCal, my battery was deader than a door nail, so that was replaced last night. On my way to Reno to pick up a moving trailer this afternoon, my nice new battery died 20 miles east of Reno, leaving me stranded on the side of the I-80. Fast forward to this evening and my bank account is close to $700 less than when I started out, between the tow back to Truckee and a shop that was nice enough to stay open past 5 to replace the alternator. I'm running out of money to fix this truck and plan on selling it when I get back to Oregon. I just need it to pull a small trailer in the next day or so.

I've read through a number of questions similar to mine and the responses provided, but none of them mention having a K & N air filter, which I have. The responses I've seen range from plugs and coils to the O2 sensor to the coil pack. My suspicion is the mass air flow sensor, but that's only because it has caused similar issues before on 2 previously-owned Ford explorers. I plan on taking the truck over to Auto Zone (where I bought the battery last night) and have them pull any codes that show up. My initial plan was to go for a tune up first thing in the morning, but apparently that may not fix the issue.

I guess my question is this: with a K & N air filter on it, I can't say for sure that I know where the MAF sensor is. Is there a difference with the K & N filter?

 

You describe a classic COIL failure.
Do the following with the motor off.
With a Scanner, go to mode 6, test 53.
Scroll through all 8 cylinders looking for one with high misfire counts.
Replace that coil.
.
This type failure does not code.
This type failure causes stumble in OD and light throttle until a down shift occurs. You won't feel it any other time.
The coil has shorted turns and was precipitated long term by engine heat.
Why is an extended explanation.
Good luck.

 

It could also be the fuel pump. Going uphill requires an increase in fuel flow and if the pump is weak the engine will sputter.

 

Your K& N filter may cause a issue. More on point is that the oil for your K & N is the issue , that oil can cling to the MAF sensor and give you very poor runability problems. Generally harder starting or longer starter time. The MAF sensor is located just behind the filter box and well before the throttle body, kinda on the lower side of the tube. A quick spray with some cleaner that is safe for MAF sensors should do it.

The previous replies are really on target with what is probably going on. ( see post 2 from Bluegrass 7 and 3 from alloro)
The Autozone scanners probably won't pick up the misfires, that Bluegrass 7 refer to in post 2. that mode 6 that take higher end scanner.

If you have not changed sparkplugs for some time it would be good to do that now with new spark plug boots and springs. A new fuel filter would not hurt either. Even if you plan on selling it soon. Those who will be looking at it will see it as something they will not have to. ( well maintained) You can use it as a selling tool and maybe get more out of it too.
Shucks you might like how well it runs afterwards and decide to keep it??