low hot water in the bath tubs?

In both tubs/showers we are experiencing low hot water volume. There is no problem at the faucets ... the hot water is too hot. The water controller is a single handle in both tubs and I checked to see that I had installed them properly when replaceming them for leaks. The house is 13 years old. I would welcome any ideas why showers are luke warm while sinks are sizzling?

Brand on this valve will help figure it out, was there a temp limit setting in the valve under the handle area?