I'm a recent 2LT appointee (former SSG). I'm told I will have to work HARD at transitioning from an NCO. What "exactly" does that mean?

It means you will have to take a course on how to NOT read maps correctly. Really if you weren't ready to be an officer you wouldn't be one. Some of the best officers I had were NCO'S first. You have a huge jump on any brand new 2LT. Through your own hard work you have already achieved SSG, they don't give that away. You already know how the Military works and what is expected of you. You have a better understanding of the soldiers under you for having been one already. Don't second guess yourself, just lead.

May be different in the Army vs Navy but if it is a real problem it might be in your interaction with enlisted. It also may be someone who is jealous of your success. Congratulations on your commission.

Trying not to be a smarta$$ but you have to sometimes put common sense aside. I found myself an many situations were I was thinking like a soldier not like how the general is thinking. Ever painted an entire motor pool a different color because the brigade commander misinterpreted the direction of the CG. Only to be asked by the CGwhat the hell did you do. Patience will be a virtue.