i havent solved it yet sashco, but am going to get a lot of screening "sock" today so we can screen from interference. we think that interference and possible bad earthing could be the problem. check back with me in a couple of days

I'm also signing on to hear of a possible remedy.  I have this problem with my new plasma table, but only in the Y++ direction - everything else seems to perform fine.  I can get rid of it by increasing the step pulse setting to 5 under config->motor tuning, but that's not the way it was tested and setup by my manufacturer, so something is amiss.

ok, i will post mu findings once we sort it out...glad to know we are not the only ones with this problem. something we have noticed though, is that our step and direction signals run past a mqain power line...check that out!