I lost about 1" on my overflow tank in about 10 months. it used to be at the COLD fill level when cold, now its about an 1" lower.

I assume this is normal. I dont see any external leaks and am on my 3rd Set of LIM gaskets...first failed for unknown reasons.then the second set was OVERTORQED and lasted a week, and the 3rd set are the metal framed gaskets, and have been on the car about 60,000 miles.

I got worried since I got a LOW COOLANT warning on my DIC. I'm assuming its a bad sensor, since I did not see a sensor in the overflow tank that I remember.

That might be safe to assume was normal loss to evaporation. I think my wifes car was down about the same after a year.

Have you checked the coolant level in the radiator? I've seen it where there is a fair amount of coolant in the expansion tank, and still the radiator was low on coolant.

If your radiator level was low with coolant in the overflow that would indicate a failed radiator cap or overflow hose.
When the weather turns colder expect the coolant level to contract some.

Are you positive you have metal frame gaskets? Even Sonoma couldn't have put them on since they've been available and gotten that many miles.

An inch over that timeframe isn't anything to worry about. Refill and keep a closer eye on it.

If the problem persists with that number of lower intake gaskets, I would start looking at having a machine shop check surfaces etc.