I have a 2.5L V6 which hunted at low revs but was fine at high revs. Why?

What is your question?

I've got spark.Changed fuel filter. No luck. Was driving along when car cut out. Tried to restart, fired but at low revs felt like it was hunting. Revved it to 2000rpm & higher & it seemed fine. As soon as I put it into gear ( automatic ) so it was under load started hunting again then stalled. Managed to do this a few times but now it just cranks over but does not fire. Any help appreciated. Cheers