I initiated a donation to my church through my bank on Dec 30 2016. The transaction did not clear/process until Jan 3. Can I still count it towards a 2016 donation?

[jntbro]

The same thing happened with a mortgage payment I made on 30 Dec.

[Opus 17]

Yes for both, assuming that you had funds in your account, and that once you initiated the transaction you had no way of calling it back.  (If you set up the donation on 12/30 but you added a processing date of 1/3, or if it was cancelable before 1/3, then it doesn't count.)

Your church treasurer may or may not record the donation on your statement for 2016.  The bank probably won't record the payment as interest paid in 2016.  You can still deduct both, but remember to keep proof (you will need the interest amount from your mortgage account or statement) and remember that next year, you will need to reduce the amounts reported on the 2017 forms by the amounts you added this year.