Scorpion not holding z

My shop has an ez router scorpion 4x8 table run my Mach 3. Recently, the Z axis started stepping down on it's own with each pass..While in operation and when put into free hold, outputs 1 and 3 flash red on the diagnostics screen. No trouble code on the z axis controller in the control box. I have checked and rechecked all wires and connectors for the servo motor and encoder. Found no damage. Replaced the pin cable between the computer and control box and the condition still persists. Any ideas of what the issue is?