Michael,

I am no authority but I would hazard a guess you've been playing a lot, perhaps even with sweaty fingers, and that has had more impact on your tonality than the tuning.

My experience playing for days on end in DoubleD tuning is that it deteriorates the tone about at the same rate as playing a lot in ordinary (EADGBE) tuning.

But I'd be interested to hear if Rick or other masters have something to say on this one!

A