[wiswind]

I was NOT able to locate the power brake booster check valve in the aftermarket for my '96.
You may have to go to the dealer for it.
It was included with the power brake booster units.....but you do not want to replace the whole thing for this little, easy to replace part.

Another possible cause is a sticking Idle Air Control (IAC) valve.
When you move your foot over to press the brake, the computer takes over the idle speed by opening the IAC to keep the engine from stalling.
Stalling is the MOST common failure under this condition as the IAC sticks and does not open fast enough.
However, it is possible for it to stick in the other direction.....causing a idle speed "overshoot".
This is not a common thing, but is possible.
Cleaning the IAC would be something that I would put on the list.

The problem can be made worse by the fact that the transmission is downshifting.
A sticking Torque Converter solenoid can cause this.
Solenoid being a fluid valve that the computer activates....electrical signal to open/close it causing fluid flow that engages or disengages the torque converter.
In this case, you get a boost of power because the transmission is engaging when you don't want it to.
This "should" cause the O/D light to flash or the Check Engine Light (CEL) to light (and stay lit) when it happens.....storing a code that tells you that this is what happened.