Why it is hard to sight-read on mallet instruments...
I did a session the other day where I had to double a very specific part. It seemed like an easy pattern, but it changed in subtle ways over time. I was presented with 2 charts: one was a straight printout of the part - no repeats, lots of funny 16ths notes & rests, 6-pages long. The other, a chord-chart that showed the form (AAB, etc.). Even though the musicians involved were experienced pros, nobody spent much time on the chart. This is a very common situation now, as so much music originates out of computer files.
So I had no choice but to read down the midi-part printout, which was a rhodes thing I had to double. If I took my eyes off the music for even a second, I would never find my place again. It occurred to me that us vibists have no choice except to develop really GOOD peripheral vision for these situations, and then just HOPE we hit the right notes! IMHO, this is really a skill to work on if you wanna improve your site reading.
For years, I thought that I was not a very good sight-reader, compared to other musicians. Over time, doing it more I got better. However, I really think vibe players are at a disadvantage when sight-reading since we cannot FEEL our instrument. Sure, drummers use sticks also... but it is not quite so hard to hit a drum while you are looking at a page. Vibe bars are a much smaller target (and drummers don't have to worry about accidentally hitting an Eb on a Dmaj7 chord). Almost every other instrument, you touch it and don't really have to LOOK at it.
So have no fear if you are practicing hard at improving your reading - vibe players must keep at it. I suggest trying to work on "knowing" where the bars are, without looking down. I remember that in a past thread we did even talk about a blind vibes player who could do this -- but I am pretty sure that he wasn't a good sight-reader!