Great question, Dave.  There are of course plenty of OT uses of three that seem merely to give a certain emphasis to things, where one occurrence of a term wouldn't have the same effect.  The Trisagion (thrice holy) may be the most famous.  Commentators often muse that the phemenon may also be related to the Deuteronomy 19 stipulation that a matter is confirmed by two or three witnesses.  And, whether or not there is a Messiah figure in this text, if someone does stand after three days, whatever that might mean, it could easily be an echo of Hosea 6:2.  Davies and Allison think large parts of Matthew are made up of triads and it is the most Jewish of the four Gospels.  But if you're looking for me to speculate as to anything specifically Trinitarian, I won't, because that would go well beyond anything that could be demonstrated.  :)