16 Sierra Denali 5.3 - brake issue cause ?

[MRSUIT]

I have a problem that seems to be getting worse.  When at low speed in reverse the brake pedal will vibrate and sink to the floor.  I did have the booster recall done which was just the reflash.
 

Say your parking and you back up slowly and then when you go to stop so you can put it into park or drive when I go to stop it ( almost always now ) the pedal goes loose and as it’s sinking to the floor it vibrates.  
 

This has happened 1 time in forward which was also when parking.  Other than that it is in reverse only.  
 

Does this sound like a vacuum booster issue or any ideas ?   Any help is greatly appreciated 

[silveradosid]

it sounds like you have a faulty wheel sensor, at low speeds it stops sending a signal and triggers the abs. this is why the pedal vibrates and sinks to the floor

[discgolf01]

9 hours ago, silveradosid said:

it sounds like you have a faulty wheel sensor, at low speeds it stops sending a signal and triggers the abs. this is why the pedal vibrates and sinks to the floor

Agreed.  I had this same issue on my 2005 Silverado, but happened at low forward speeds like when pulling into my driveway - was a defective wheel speed sensor on one of the front wheels.