Bridgeport Steppers with API 260 drives

Anyone running a Bridgy on original motors with API 260 drives in
parallel at the full 8 amps?
I have seen some posts where people are using them in series but not
parallel.
I have one here that trips out sometimes on firts strt up and
sometimes after a few minutes.
All four drives are doing this and there is no consistancy to it.
Power supply is 58 volts DC.
Swopped spare API drives into the circuit but same thing, could fault
out at any time.

John S.