small servo motors keep stalling

Hello...I have been trying to get my little Taig CNC mill going..I have a
servo motor setup with little pittman motors. they say 24 volt, 5:9 ration and
coupla other numbers..im not sure about the rpms.The whole setup is from
a cnc retrofit company so it is not "homebuilt"at least by me , but the tech
support has not been able to help me figure out why my motors keep
stalling out at the SLIGHTEST bit of resistance....the gibs must be all the
way backed out for the motors to not stall.....i havent even tried to mill
anything....the taig has a 1/2-20 screw--no ballscrew--and i have a
direct/staight coupling to the motors using interlocking spiders with
plastic piece in the middle of the spider to accomadate axial
misalignment...backlash is about .003 in Y and Z and .01 in X..just
wondering if could get ANY sugestions or help....do i need to change to
belt drive ? Tahnks for any and all help Mike