Two more things to check.

I had similar problems a while back, and finally discovered that I needed more tension on my jib luff (more backstay). When I turned up, the jib would luff and shake a little, and this slowed the boat to a stop just before passing through head to wind. I was also raked too far aft for the breeze and it was hard to get the boat to bear off when I did get through the tack. I was used to sailing planing dinghies where we raked the rigs back in a breeze... exact opposite of what displacement hulls do.