Danno,

If your jib remains cleated and backwinded for even a second, it will stop the boat. Make sure that as soon as the jib collapses when it gets close to the wind that it is uncleated. The timing on moving the jib is important - too soon and you are loosing valuable speed into the tack - too late and the jib will push the boat backwards. As the other folks said too - don't put the tension back in the mainsheet until the boat is moving and you are moving your weight forward again. You want some twist and belly in the main while the boat is accelerating back to full speed.

Your weight placement on that boat will probably be important too. Make sure you have the crew weight as far aft as possible when tacking. This will help to lift the bows clear of the water so they don't have to push a lot of water as they turn. To see this affect exagerated, turn hard while reaching and you will see how much water the bows have to push when turning. Moving your weight back will lift the bows so the boat doesn't encounter quite as much resistance while it turns.