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The new inquiry/hard pull for the mortgage pre-approval could be what's doing it. I took a 25 point hit on one of my credit scores for my "pre-approval" HP in December where there were no other changes. The other two stayed steady. I don't see anything else in what you've described that would explain a decrease - only an increase in your scores.
So, to update everyone... My lender pulled my trimerge from equifax today and he got a 729! Needless to say, I was pretty pleased. thanks for everyone's insight.