Today, I noticed my truck (6.7 with 170k miles) blowing black smoke from the exhaust during mid-acceleration. The truck is stock except for aftermarket intercooler tubes. The turbo seems to be building PSI normally, and I haven’t noticed any change in fuel economy. Any suggestions on where to start troubleshooting?
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My friend’s newer 6.7 engine emits a brief puff of black smoke during heavy acceleration. It is not rolling coal, just a noticeable puff.
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This is not typical unless it’s been removed. The truck owned by OP is stocked. There must be no smoking.
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Does the DPF still come on your truck, if it is still stock? If so, one of your truck’s problems is that your DPF is cracked.
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The cracked DPF was a frequent issue with the earlier 6.7L engines, to the extent that a Technical Service Bulletin (TSB) was released addressing it. I can’t recall the TSB number, though. 
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Change the fuel filters first before doing anything else.
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It was, in fact, the air filter. 
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While most people don’t forget about air, I don’t think changing the gasoline filters would be as effective as doing so. However, fuel is something that is constantly forgotten. The first guideline of car maintenance. Check the air delivery and gasoline 
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I change the fuel filters every 5,000 miles along with the oil and usually swap out the air filter at the same time. However, I was on the road recently and forgot to bring a replacement air filter with me, and then I forgot about it once I got home. My current fuel filters have 3,000 miles on them. My goal is to get 500,000 miles out of the truck before replacing it. While 500,000 miles might seem ambitious for a stock truck, I have heard of them reaching over a million miles in stock form, so I am extremely meticulous about maintenance. I don’t get why people always blame the DPF system or the CP4 pump when issues arise, I think both are well-built and not as problematic as they are often made out to be.