2015 Tahoe LTZ - intermittent brake assist loss at low revs - vacuum pump??

[2015LTZ]

there is another known issue of the vacuum pump seal going bad and allowing oil into the brake booster that can cause a problem and yet another issue where the booster seal can leak
there is a service bulletin for the booster leak

https://static.nhtsa.gov/odi/tsbs/2016/SB-10081053-2280.pdf

there is a 10 year special coverage on the vacuum pump "if" IT fails diagnostics and or throws a "service brake assist" in the dic therefore setting a code.
https://static.nhtsa.gov/odi/tsbs/2019/MC-10167479-9999.pdf
I would pull the vacuum line off and check if there is fluid inside or if it is dry

If the vacuum pump fails diagnostics it's free under the special coverage for 2015-2018 for 10 years

Checked the lines, no fluid. Also fluid inside the booster is clear, no oil there.

 

[Ibustbravo]

Yea there's a vacuum pump on the right side of the engine. It's a real pain in the butt. When I rebuilt my engine I plugged the holes in the block; for a future turbo install, and routed the line from the brake booster into the intake manifold. Pretty easy fix. I guess you can call that a 'vacuum pump delete'

 

[Doubeleive]

Checked the lines, no fluid. Also fluid inside the booster is clear, no oil there.

I re-read your original post, you might want to check your front hubs. if a hub or "hubs" are wearing out this can cause both your noted symptoms and the noise (noise while wheel is spinning anyway)
jack up the front so the wheels are off the ground and see if the wheel has any play at 12 & 6 it should have none, you can also check 3 & 9 but there will be a little normal play there because of steering, you can also spin the wheel and listen for any noise, should be pretty much silent.
a vacuum pump issue would be pretty unlikely to cause a abs activation, but a lazy abs wheel sensor would and that normally is because of hub wear but not 100% always a sensor can be bad as well but is less likely.

 

[OR VietVet]

I gotta wonder why they need a vacuum pump on a stock engine, for brake boost? Are they just adding to the inches of vacuum just to cover something?