I have a 3 amp stepping motor on my x axis it runs well with jogging and with single g00 and g01 moves. Although it growls when I use feeds less then 20, it still moves correctly.

When I execute the following coordinated movement it jitters, growls and misses steps:

G0 G49 G40 G17 G80 G50 G90
M6 T0(TOOL DIA. 0.4375)
G64
G20 (Inch)
M04 S0
G00 G43 H0 Z0.5
X0 Y0
G01 Z-0.0040 F10
G2 Y0 X0.2625 R0.1313 F10 <- movement is fine here
Y0 X-0.2625 R0.2625 <- errors and noise start here

...

Any ideas?

You might try modifying your post so that it outputs all gcodes for every line. Try putting G2 in front of that line and see if the controller can interpret it better.

You're machine may also have to much binding, so it's requiring more torque than your steppers can supply, theirfore the missed steps.

I thought of that but when I just issue a g00 or g01 command with the same load it works fine.

Try writing the second command out in full so it looks like the first including the feed. That is a test rather than a solution.

Also try running the first G2 with the coordinates of the second to see if it still works ok.

Graham