[73 Mustang Boy]

The other day I changed the points, rotor and cap on my car. I also tuned it up good. The timing is set at 12* and it idles smooth and runs great. The only problem is that when the engine reaches 2100 RPM's the ignition misses. You can realy feel it if you accelerate through 2100, only if you try and hold it there then it misses real bad. The only reason I noticed it was because my car turns 2100 at exactly 55mph. The strangest thing is the engine will run fine at any other RPM even 2200 all the way through 5000. I am stumped any ideas would be apreciated.