I feel the same thing in my throttle, but like the other gentleman said, i found it to be because of the difference in the curvature of the linkage on top of the valve cover.
The bushings riding this "curve" will also wear with time and cause the feeling to be more pronounced in addition to not giving you full throttle. Such was the case for me so I adjusted the throttle linkage in order to compensate for the wear to acheive full-throttle once again. I tried (not too hard) to get the bushings, but nobody had them that I could find.
Have fun, Adam