Thanks Swarfing
Sorted now
Having tried everything i could think of including deleting and reinstalling mach3, running the pulse testing again (excelent) i decided to try a different PC and wow what a difference.
beautifully smooth traversing right up 9000mm/min
it must have been a hardware fault or was being interupted by something else.
i had been using that pc for about 9 months on my first attempt at building a cnc (MDF special) so you have to wonder how much it was effected. although it was monumentally slow anyway due to the rigidity problems inherent in such a build. (but it gave me the bug!!!!)