Hello Tom, and welcome. I also own a 06 Discovery. Mine is a 39L. Our rear AC (Zone 2) does not blow as hard at Zone 1, but it is more than a trickle, and cools OK. I do know that each zone can be set for cool high or cool low and can be set for fan only. I know you stated that both zones are set the same. Here is what I suggest. I belong to a group called DOAI "Discovery Owners Association" it is for Discovery owners only. I joined 4 years ago. This is a great group of very knowledgeable owners from all walks of life that can assist you with any issue. They have a forum that is second to none. You stated you are going to have many questions. DOAI is where you are going to get your best advise. You can find the group at www.discoveryowners.com
Our coaches are very similar. I have 4 slides and you probably have 3. I would bet our paint schemes are the same. If you wish to talk off line let me know. I will help anyway I can.
Jim Pinkerton
2006 Discovery 39L