I'm writing the lead part for my own song and i want a tremolo on a different string other than the low e string (easy), but i can't seem to get the same speed and accuracy i can by just doing it on the low e string. any tips?
"One good thing about music, when it hits you, you feel no pain."- Bob Marley
Sounds too easy, but you just have to do it over and over and go slow.

I seem to subconsciously move my palm down just slightly if I'm fast picking the A string and move my whole hand for the higher strings.

Also, I anchor my pinkie finger just below the bridge pickup. This allows your wrist to go crazy while keeping your hand in place. You have to make a conscious effort to do it at first, but will eventually just be automatic.

Even after years and years of playing I'm not as good on the higher strings either. It's just because a lot of the songs I learned first had that palm muting, fast picking, low E thing happening...so it's a habit.

If your an "elbow guy" and move your whole arm, it's going to be harder. I would get out of that habit asap. Try not to be that guy.
thanks for the advice and yeah i'm trying †o break the habit of moving my whole arm
"One good thing about music, when it hits you, you feel no pain."- Bob Marley
Agree 100% about the elbow thing. Even though it's initially easier to pick fast with elbow picking, you can't get the level of control you need that way to play harder stuff. Also, it's hard on your joints.

About the anchoring, I'm going to give you a contrary view. I'm not looking to start an anchoring vs no anchoring argument here, just sharing what I've learned in my experience. First of all, by "anchoring", I'm talking about actually planting a finger on the body of the guitar or the bridge and using it for support. I don't consider letting your fingers hang below the strings and having light contact with the body of the guitar to be anchoring because there's no "anchor" that you're pivoting around.

Anyway, in my opinion heavy anchoring will hold you back in the long run. The reason is due to the mechanics that should be going on as you move from string to string. The idea is to move your hand as you go from string to string, so that the relationship of your thumb/index/pick to the string you are playing on is always the same. Then you are learning the same wrist motion and picking technique regardless of what string you are playing on. The only adjustment you have to make is for the guage of the string. If you don't do this, you have to learn to pick effectively at all these different angles and you have to change it as you play and go from string to string. It sounds like this is why you are having trouble tremolo picking on the higher strings. If you anchor heavily, the planted finger can get in the way of freely moving your hand from string to string.

Hope this helps. And to the guy who suggested anchoring, again - I'm pretty open minded about this stuff. If you've find a way to get it to work for you to where it's not holding you back (and it's definitely possible - look at Michael Angelo Batio for example), then it's all good. I just wouldn't recommend it with all other things being equal.