What firmware are you using, Repetier at least has a bug in it, the steps/mm must be set correctly both in configuration.h AND in the EEPROM settings.
If they do not match you get weird motion, the issue is that the actual delta calculation uses constants derived from the configuration.h settings, but the motor motion is based on the EEPROM values.
If they do not match you get weird motion, the issue is that the actual delta calculation uses constants derived from the configuration.h settings, but the motor motion is based on the EEPROM values.