shifting problem

:jerking: i cant figure it out, i need your help please. I have a chevy venture 2000 model with 200000km on it. i have an on and off problem with my brake pedal only when the van is not moving. sometimes it is very hard to press so i wasn't be able to shift the gears, from park to drive or vice versa. any help will be appreciated. thanks

Check the vacume supply to the booster, see if it will hold vacume, it may be bad.