05 F250 Powerstroke FX4

I am still new to this truck and trying to figure out a problem that I seem to be having.

My brakes are doing this weird thing where the pedal does not feel like it wants to go down and you can feel the pedal pulsing a little bit. This always happens after I get on it (drive it like I stole it) and or kick it down to break the rear tires loose.

Normally, the pedal goes down like a normal brake pedal should. However, when this situation happens, the pedal only goes down a little bit...feel the slight pulsating action (get your minds out of the gutter) and then the pedal will go on down like normal. Unfortunately, I am not getting normal braking distances...

It feels like the brake fluid so you get the resistance from the fluid is being ran through a funnel that is full (when the pedal doesn't go all the way down). However, little pockets of fluid are passing through the funnel (the pulsing) and then the line clears and the rest of the fluid can be pushed through....

I know that sounds stupid - or weird - but hoping someone knows what is going on.