So - just noticed this section -

<Vel0>6.667</Vel0>
      <Acc0>200.</Acc0>
      <Steps0>320.</Steps0>
      <Vel1>6.667</Vel1>
      <Acc1>200.</Acc1>
      <Steps1>320.</Steps1>
      <Vel2>6.667</Vel2>
      <Acc2>100.</Acc2>
      <Steps2>320.</Steps2>

Is the Vel* the feedrate?

I am pretty sure it shows as 4000 in the GUI, but 6.667 here?

there are other programs that will make M3 act that way .. firefox is one . if I have it  loaded with M3 the feed is very very slow.
make sure nothing else is running in the background. I have heard of other prgms that don't play well with M3 either. quicktime hides in the background and causes issues too.
Chuck Smalfus