I agree with Mike9241 that TurboTax doesn't seem to handle donations of stock very well. There are questions it should ask that it doesn't ask, so it is effectively making assumptions that might or might not be correct.
I have answered your questions below as well as I can with the information that you provided. More details are needed to be able to give you more specific answers, especially concerning how to make the entries in TurboTax.
Are you using TurboTax Online or the CD/Download TurboTax software? If you are using the CD/Download software, are you entering the donation in the Step-by-Step interview or are you making entries in forms mode?
You said you paid tax on the dividends over the years. Did you take the dividends in cash, or did you reinvest the dividends in additional shares of the same stock? Have you previously sold any of the stock prior to making the donation to charity?
I assume that the stock is ordinary stock that is publicly traded on a stock exchange, and that it is not a mutual fund. If that's not true, provide details.
(1) Form 8283 asks "How acquired by donor" Was this acquired via gift or purchase?
Technically, if your father put money into the custodial account, then used the money to buy stock, you acquired the stock by purchase. The money was the gift. It became your money as soon as it went into the account. But if your father owned stock and transferred shares that he owned into the custodial account in kind, then you acquired the stock by gift. Any shares that were purchased with reinvested dividends were acquired by purchase.
(2) If gift, turbotax does not give me the option of entering gift, only purchase. How do i enter it as a gift?
For practical purposes, I don't think it matters whether the stock was acquired by gift or purchase. Your deduction is going to be the same either way. Since designating it as acquired by gift in TurboTax is not straightforward, it would be easier to just leave it saying purchase. (The situation might be different if your father transferred shares in kind, so that the shares were a gift, and the value when you donated them was less than what your father paid for them, but that's an unlikely scenario for stock that was purchased 40 years ago or more.)
(3) Is my deduction the value of the stock when donated or the value of the stock when my dad bought it in my name back in the 80s?
For any shares that you owned for more than a year before donating them, your deduction is the market value on the date of the donation. You were the owner of the custodial account from the beginning, so all of that time counts as time that you owned the shares.
You may have owned some of the donated shares for a year or less because they were purchased by reinvesting recent dividends. You would have to enter those shares as a separate donation because the rules for the deduction are different. The deduction for shares that you owned for a year or less depends on whether the value on the date of the donation was higher or lower than what you paid for them. If the value on the date of the donation was higher than what you paid for them, your deduction is the amount that you paid to purchase them. If value on the date of the donation was lower than what you paid for them, your deduction is the market value on the date of the donation.
