What do you mean with church music? Is it like chorales and stuff?
Could be a music reading issue. If you are improvising, you might not be actually reading the music in detail, playing exactly what is written.The hymns might have simpler chords. The classical pieces might throw in something a little more and that could throw you off.The classical music could just be a different style.I wonder what your expectations are. To play a classical piece perfectly the first time you sit down at it? Something like that would be my guess. If you can improvise, you've got some solid skills down. Just work on preparing a piece then.
Improvising church hymns and playing classical piano is like apples and oranges. I was a very good classical pianist before I ever started playing church music and when I started at church I found it difficult to make it sound good even though the music itself was fairly easy to read. Then my improvising improved and I began to make the hymns sound good. Of course this was also around the time I stopped playing classical music for a few years... I found I could sight read hymns and come up with beautiful improvisations, but when I went back to classical my abilities had suffered greatly due to lack of practice. The stuff is very different both technically and musically.I think you may be setting your expectations too high due to being so good at playing church music. Have some patience and don't expect the classical stuff to sound perfect right away. With time and practice I'm sure you will see your abilities at classical music improve greatly.
When it comes to church music...I can sight read and play anything you give me. I improvise and come up with some great arrangments. However, when it comes to Classical Music, I feel like I'm 8 years old again trying to learn how to play.
The stuff is very different both technically and musically.
i'm the exact opposite. i've studied classical music for a long time and i have some experience, but when it comes to any improvising or sightreading i'm absolutely pathetic.