The guy below is incorrect.
A gift is exactly that, a gift. He must sign a letter stating no repayment is expected.
A secured loan (or "collateralized loan") is a permissible source of funds for a gift. Dad would need to provide a copy of the note from the loan against his truck, plus a copy of the proceeds check and proof he deposited it into his account before gifting it to you.
It's a heck of a paper trail, but it is permissible under FHA guidelines. Here are the pertinent guidelines:
If the gift funds are being borrowed by the donor and documentation from the bank or other savings account is not available, the Mortgagee must have the donor provide written evidence that the funds were borrowed from an acceptable source, not from a party to the transaction.