I know i haven't responded for a while, but i've learned a little more about the problem know
I'm starting to think that is more along the lines of the filter like you say.
However, What i've noticed now is that, i can go full out in D and have no problems, but when its in OD, and the revs get up there is when the problem comes back.
Possibly the way it routes the fluid in D, stop it from starving?
I'll have to do a fluid and filter change and see where that gets me.
Thanks for the help