Have you done anything with the bypass valve(s) behind the water heater, that is allowing cold water to mix in with the hot water line (this is very common). This will make the hot water seem to run out quicker.
Also, another culprit that can allow cold water to mix in with the hot water line, is when you leave the outdoor shower taps on, but cut it off at the shower wand head instead.......and forget about it. I would check this too, along with the bypass valve being completely shut behind the water heater.
2011 Flagstaff 831 RLBSS
I used to be addicted to time travel, but that's all in the past now.