DCP,
I watched this thread for a while before responding. Being an instructor, I have had this happen before with my students. WIthout comparing experiences I will point out two basic areas of the student/teacher relationship that are vitally important to make that relationship work.
The first is patience. The instructor needs to be patient with the student to allow the student to develop and mature at their own pace. Patience is also required of the student. Alot of what we do as instructors is trial and error. We assess, diagnose, prescribe a remedy, evaluate it, and if need be - we go through the process a few times before we get it right.
Many times if something is changed in your stance or stroke, the flaw being corrected is powered by bad habits. Not only must the flaw be dealt with, but you also must address the habits linked with the flaw. This does not heal itself overnight. Sometimes it takes a while. The pain you are experiencing can be merely "growing pains" as you struggle to unlearn the old habits. That is just part of the process. The new habit needs to be planted like a seed. It must be nurtured and cared for properly for it to grow. At first the seed will sprout and it won't be very strong, but overtime it will grow taller and stronger. It is the same with any skill you apply to your game. When you understand this process, then you will understand why patience is a two way street in this relationship.
The second is trust. As a student, you should trust not only the instructor (in this case Mark Wilson) but you must also trust his words, his knowledge, his judgment, and his methods. You basically gave him your stroke/stance and put faith in his abilities as an instructor to make it better. If you are questioning his judgment now, then your faith in him has been weakened. So has the faith in everything he showed you.
This means you now have a choice. You can either toss it all aside and look elsewhere for instruction - OR - you can take measures to re-establish and stengthen your faith in everything that your instructor showed you. It is my advice to NOT take the easier softer way. A lot of times our character building is lost in our rush for comfort.
I would say talk it over with Mark before talking it over with people on a pool forum. Here you have a chance of getting advice that feeds the growth and strengthening of your game, but you also run the risk of getting advice that will feed and justify the bad habits that will continue to send you down a path of disappointment. Take a few days off, catch your breath and start all over again. Sometimes that's all you need. You made a great choice in instructors and in my opinion you made a fantastic investment in your game. Make it count.