Symptoms
"Increased brake pedal effort, hard brake pedal, and/or potentially increased stopping distance" — GM's own wording. The brakes still work; what is missing is the assist, so the pedal feels wooden and needs a much harder push. It shows up first at low speed and light braking, which is exactly the situation where a test drive on an open road will not find it.
Likely cause
GM told NHTSA the pump failures traced to "foreign debris such as oil sludge in the engine oil" clogging the pump's inlet filter screen, which starves it of lubrication and cuts the vacuum it can make. If that is right, then oil change history is not a side note on this truck — it is the mechanism. Ask for records.
How should it be checked?
Two separate things to confirm, and they are not the same thing. First, the recall (NHTSA 19V-645, GM N192268490): the fix is a reprogrammed brake control module that leans harder on hydraulic boost when vacuum drops. It changes what happens when the pump weakens; it does not replace the pump. Second, GM's special coverage N182202780, which does replace the pump — 10 years or 150,000 miles from the date the truck first went into service, regardless of who owns it. A 2016 truck reached ten years in 2026, so on most of them that window is now shut and the pump is the buyer's cost. Check the VIN on nhtsa.gov/recalls for the recall; ask a dealer for the coverage and repair history.
How can you check it yourself?
Brake gently from low speed several times in a row, in a car park rather than on the road, and feel whether the pedal firms up as you repeat it. A hard pedal after the engine has been running is the sign; a hard pedal before you start the engine is normal and means nothing. Then check the VIN on nhtsa.gov/recalls — if 19V-645 still shows as open, the reflash was never done.
The question to ask the shop
Has recall N192268490 been carried out, and has the vacuum pump itself ever been replaced under special coverage N182202780 — if so, at what date and mileage? Separately: what does the oil change history look like, and how far apart were the intervals?