i have changed cylinder head,dizzy,leads,plugs,different throttle body,changed oil and filter etc to cure a missing problem, now that has cured itself ang gone i,m left with a hesitant polo, if you come off a slip road for example and overun in top and then change to third and put your foot down slowly to pull away again you get one/two or three spits and kangarooing and then once over that rev range it accelerates away like a good un all the way to maximum, I've checked vac hoses and rubber base gasket and even used hermetite on gasket to help with seal, but still have this annoying problem, please help

sounds like an ignition timing thing to me, remember that when you go onto overrun the engine is pulling a huge vacuum..