Hi seniocs,
I used to encounter this problem, but now I have overcome this problem.
Firstly, you need to practise sight-reading daily. Try to do a few pages or exercises.
pls take note of the key signature, any changing of key etc.....
try to read ahead and don't pause if you make a mistake, just continuing to keep the music flowing.
rhythm is important,always keep in time. If you can,add in the expression.......
I feel that Paul Harris's sight-reading book is good. You can purchase one for your grade.
Lastly, practise makes perfect. Always sight-read if you can, for e.g playing a brand new piece.
Czaire