We received a car as a GIK valued at 24,300.  We recently sold it for $20,000.  Should I change the GIK amount?  If so, should I just make a note that it was valued at more?  Right now it still comes up as $24,300 but that isn't the cash that we received so our books are going to be off.

I would adjust the gift.  That way you can change the gift, but keep the history of the original value and note why the gift amount is different.

Did you own the car for more than 2 years?   if so don't change anything but if you did't have it that long, the value to the donor is the Fair Market Value/Price realized.  Do an adjustment to the gift (down to $20,000), explaining in notes that the car sold and send a new letter to the donor stating that you sold the car and the "price realized' was $20,000. It is up to the donor and his/her tax advisor to make the change on his records.