cutting out, sagging missfire

been running my 88 cabby now for a couple of weeks but it seems i still havn't sorted the missfire probs, it still missfires after changing gear and then taking power but not all the time and when you are running and you take your foot of the throttle it seems a bit lumpy, also if i brake hard to a stop the engine wiil cut out alltogether but will re start straight away, it runs nice rest of the time but not sure if it should be a bit more responsive as i have only just started to drive it, any ideas have done fuel filter and replaced both fuel pumps for genuine new ones, also the lift pump sounds strange when you lift off the throttle.

Co2 mixture, you may have to take to garage to get analyser on it.  Before you do that though, take distributor cap off clean the contacts and give it a burst of WD40, clean HT leads ends.

ok mate thanks for reply, i have replaced the dizzy, rotor arm, plugs and leads so think the next thing would be checking it on a machine, thats if i keep it long enough its cost me an arm and two legs so far think it will have to go.