It may be that the 7344 is missing encoder values, or that the motor isn't tuned correctly. The first thing I'd like for you to check is that the Encoder Counts per Revolution input to the Axis Settings menu in MAX is set correctly (I believe it defaults to 2000 counts). To check this, you can rotate the motor by hand one revolution to see how many counts have accumulated. Most encoders are either 2000 counts per rev or 4000 counts per rev.
Once you have that confirmed, autotune the motors and make sure the values for Kp, Kd, and Ki are resonable. (Kd is often around 10x Kp) Once these are set, start your motors moving slowly and observe the following error. This can be seen under the Advanced tab of the 1D Interactive menu. If it is slowly incrementing, t
hen your're missing counts. If it is negative, then the encoder phases may be backward. If there is no following error, or the count stays constant, then try increasing the speed. It could just be that your encoder sends pulses too fast for the 7344 to read.
Let me know how it goes.
Kyle V