Also...since you are now using a new jib and a new self tacker, make sure there is enough of a slot between the jib leach and mast/backside of the main. If the jib is in tight but the main is out, you will choke off the flow from the jib to the backside of the main.

If the slot is closed off, or too small, this will cause the feeling that you are overpowered, but not going fast, as you described above.

If you are not sheeting the main tight enough, as Jake said, that will close off the jib/main slot as well.

The quick and easy fix is to ease the jib a little, and sheet in the main, that will open the slot. See if that helps with the speed/overpowered feeling.