Shower – Can’t remove single handle shower handle

While I hate plumbing, I do quite a lot for close friends and family. I don't know exactly what you are doing, but I know a couple of things, and I hope these will help. When you loosen the gland nut closest to the wall, you probably need to turn it clockwise. Normally when you loosen something, you usually go counter-clockwise. In this case the nut stays on the pipe, not the valve. Always you a back wrench like you were talking about to keep from twisting the pipe.

Here's a You Tube video that shows it. I hope that this helps and is not exactly what you have done before. Did I say I hate plumbing?

The troubleshooting section in the installation guide would indicate 2 things. First, you've likely backed the limit screw out too far - assuming the water pressure on the hot and cold sides are similar between the two showers, they should be set in the same range. Second (and more directly related to your issue), you should pull the spindle assembly and make sure it is clear of debris and calcium deposits.