Stalling motors?

I am new to the cnc arena and have jumped in to it with a plasma
table project. I have just gotten to the point of actual motor
movement and am unable to get the motor speeds I was expecting. I am
able to get 30ipm on x axis and 80ipm on y axis, above these speeds
the motors stop moving and sound as if they are free wheeling(I asume
this is motor stalling).My table design is simular to Thourchmates
design and the are using 135oz.in motors and claim speeds near
300ipm. My question is are the motors I have to small or is there
something else that is causing my slow moter speeds? If it is the
motors that is suspected, what size should I be looking for? Any help
would be apriceated. Hear is the info on what is used with this
table.
x & y axis use gear racks with spur gears(24 pitch 15 tooth)
both axis use 1 motor ea. and have belt reduction of 3.4:1
x axis is driven at both ends via 3\4in shaft
I'm using Mach1 and have a pmdx-120 connected to the computer
motors are from click automation and are nema 23 3V/3A 125IN/OZ
P/Supply is unreggulated 65V 6A
gecko 201 drivers with 470uF cap. and 36K res.

Any advise would be welcomed,Thanx in advance,
MONTY