I have a Glacier Bay single handle shower mixer. The wife is complaining about the lack of hot water. I have attempted to adjust the temp using the incoming valves to increase the hot and decrease the cold water incoming. This seems to have little affect on the temp. Is there another internal adjustment? Perhaps removing the mixer and adjusting.

Remove the cartridge and insoect it for any debris that could be partially clogging the hot inlet. Leave both incoming supply valves fully opened.

Had the same problem. There is a stop or limiter behind the handle. To fix, remove the rubber plug under the handle. Find the correct size Allen wrench and loosen the set screw. Pull the handle straight off the square post (you don't need to take the escutcheon plate off). Around the square post you will see serrated stops. The fixed one is the stop for off. Pull the non-fixed one out, it should just slide out, and move it over so that the handle can rotate further. Reinstall the handle.