Why isn't the hot water in my shower hot enough?
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.