[TheRedFX4]

So I just noticed this issue this weekend. I've had the truck about 2 weeks. I've racked my brain and can't pinpoint the issue, so on to the problem and hopefully a solution: when the engine is running and in park, I can pump the brake pedal and it'll stiffen up as if the engine is off. If I rev the engine and keep the pedal pressed, I can feel the pedal slowly start to soften. When I'm driving and doing normal stuff, all is well. It's only at idle, even in drive, but I have to pump the brakes a few times to stiffen them up. Then I drive or rev the engine for a few moments, and it's back to a normal pedal. Vacuum line? Booster? Thanks in advance!

 

[TheRedFX4]

Any diagnosis on it? And when did you start noticing it?

 

[TheRedFX4]

I don't normally pump my brakes, but to ease your mind, I did it today, and it goes hard as well after the 4th pump while in park with engine running.
I don't think you have anything to worry about.

That's just strange to me. First vehicle I've ever owned or driven that does that. Have you ever gotten that checked or had any braking issues?