On the motor tuning configuration page for each axis there is a box for pulse timings. I'm not sure if you can set 1.5 for the step pulse length but 2 would be fine (1.5 is a minimum). There is an internal value for pulse timing that Mach3 uses anyway and the value you give here is added on. I would be surprised if it makes much difference to your problem but it is such an easy thing to do, it's worth checking. Set 5 for the direction pulse length.

For step signal polarity, go to config->ports and pins->motor output. There is a box for step signal polarity which has either a tick or a cross. Click to change it for the axis that is giving problems.