Sounds like you might need spinnaker trim and rigging 101. Looking at how a symmetrical spinnaker on nearly any boat of your relative size and vintage will help you get things sorted out. Matter of fact, if you know anyone with a boat, or even a friend without that has experience with spinnakers, have them look things over and give you a hand. On the North Sails website, you can enter the following in their search box:
North U Racing TRIM Coursebook
This is probably more info than you need, but is a good resource. There are also a ton of other basic sailing books that will explain what's happening with the mechanics of trim.
Note 1, replace all the wire bits on your spin pole with amsteel or similar. One meathook is all it will take to tear up your spinnaker.
Note 2: the pole down haul does nothing to hold the tack to the end of the clew. It only adjusts the height of the tack assuming the spinnaker guy is pulling the tack properly to the end of the pole.
Note 3 (and less germane to the discussion given the level of experience, but

On smaller boats like the Ranger 26, you can even get rid of the downhaul and use twing lines only to control pole height. I've seen it done on a number of smaller boats, but still don't really like it as the pole with still bounce around too much IMHO.