There's no single answer without knowing the specific transmission installed in your truck. You'll need to:
1. Check your owner's manual: This is the best source of information. It will specify the correct fluid type and capacity for your truck's transmission.
2. Check the transmission itself: Sometimes a sticker on the transmission will indicate the capacity.
3. Consult a Ford parts specialist or mechanic: They can identify your transmission based on your vehicle identification number (VIN) and tell you the correct fluid capacity.
Trying to guess the amount could lead to underfilling or overfilling, both of which can damage the transmission. Always consult the correct information sources before adding transmission fluid.