Lyn-- I think clematis like a dark rich soil with organic material. I started all my clematis from bare root. My research said to keep it in a pot and not rush it into the ground. The first year I keep clipping them down to force more energy into root growth. A good root system will send up more vines, more vines = fuller plant that can support more flowers. So living in a container for awhile can make it stronger. I purposely kept mine in pots for two years before putting in the ground. I am in Texas and mine grows under a Crepe Myrtle for morning sun and dappled afternoon sun. I think you are like me... Full sun never means full sun here. Maybe I get a few less flowers, but at least it is alive and green with some shade. Try to gently open roots up with out breaking them. Although they easily fill a pot with their roots, I have not seen them get severely root bound in a pot. But if they are you may want to soak the roots and see if you can unbind them. If you can take care of roses this will be s snap.
Good Luck.
May you be blessed with success!
