With automatics,
When you stop on a hill, there is a system that turns on that allows you to move your foot from the brake to the accelerator without the car rolling away. (maybe some sort of mercury switch perhaps??). As your drive way is not level, could something similar be attempting to kick in thinking that you are rolling backwards (as you said it happens when you reverse) and it's juddering the brake attempting to stop the roll??
Update : Manual page 100
<i style="line-height: 1.4;">The system makes it easier to pull awaywhen your vehicle is on a slope without the
need to use the parking brake.
When the system is active, your vehicle will
remain stationary on the slope for two to
three seconds after you release the brake
pedal. This allows you time to move your
foot from the brake to the accelerator
pedal. The brakes are released
automatically once the engine has
developed sufficient drive to prevent your
vehicle from rolling down the slope. This
is an advantage when pulling away on a
slope, (for example from a car park ramp,
traffic lights or when reversing uphill into
a parking space).
The system will activate automatically on
any slope which can result in significant
vehicle rollback
[/i]
Switching the System On and Off
Note:The system can only be switched
onand off for manual transmissions.
Note: Once you have switched off thesystem, it will remain off until you switch it
on again.
Your vehicle comes with the systemalready enabled. If desired, you can disable
the feature
In car menu:
SELECT :
Ford Eco Mode - Vehicle Settings - Hill Start Assist - Off
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Edited by: Davis_Zadian 
