I am going crazy trying to fix my issue. 2010 F150 XLT 4.6L and getting the low vacuum C109D

This all started with my master cylinder failing (o ring failed and drained all brake fluid into booster) I replaced the master cylinder and brake booster and once I did that I started getting the "Check brake system" warning on the dash at random times does not matter if under heavy load, high speeds or just coasting. I will add I dont have any other symptoms of a issue hard or soft brake pedal, engine performance no other codes are displayed.

What I have done or replaced already
Master cylinder replaced
Brake booster replaced
All vacuum hoses replaced (I know for sure the vacuum lines for the IWE were bad)
IWE both replaced
Front wheel hubs and speed sensors replaced (they were due and since I was pulling the IWE I figured I would do at the same time )
Brake booster check valve replaced
IWE solenoid replaced and check valve
Bleed ABS module
Verified no leaks in the system with vacuum gauge and smoke test
Monitored vacuum while driving (T off with vacuum gauge) other than the drop when under acceleration no issues, I am running around 18-20hg (I am at high altitude)

Any help would be appreciated, I am going crazy trying to track this down, I hope I am just missing something simple.

 

Did you check/replace the vacuum line between the booster and intake?

 

Yep that has been replaced also, and sealed off the throttle body port and pressure/smoke tested no leaks

 

**UPDATE**

After going thru everything again it seems that I did get a faulty replacement brake booster, swapped it again and problem has been resolved.