Form 8283 is available for Efile, but there have been some changes to the reporting that may be affecting you. If you're using TurboTax Online, close the program, clear your Cache and Cookies and return to the Charitable Donations section.
Break down your non-cash donations into line items of less than $500 each. For example, if you donated $1500 to Goodwill, enter three line items of $500 each. If your total donations are over 5K, you'll need a signed statement from the donees and will need to mail your return.
Here's more info on Form 8283 and Efiling with Form 8283.