Water heater in Winter

reverse_c

Hello all. I recently replaced my hot water heater since I thought the other was the problem. My issue only in the winter is running out of hot water. 2 kids taking a shower and the 2nd runs out Midway through. 
I figured the dip tube was messed up after replacing the elements with no luck. Instead of calling a plumber I decided to just replace my out of warranty water heater.
The issue is the same. 
My only assumption in the winter is that the water coming in is too cold and the water heater (55 Gallon) cannot heat the incoming water fast enough. Considering the old water heater (50 gallonldid the same thing, there was never anything wrong with it.
Is this possible as I can't find in the web verifying this? 
Besides faster showers, anything I can do or add to the existing heater?
I guess I'm stuck with this water heater for a while. 

Larry Weingarten

Hi, What is the GPM flow of the showerhead? Possibly just replacing it with a 1.5 gpm head will fix the problem. Also, and just to eliminate the possibility, check for crossover between hot and cold. Do this by shutting off the cold supply to the heater and then opening a hot tap. It should stop running in seconds. If it keeps running, cold is getting into the hot side pipes, cooling it down.
Yours, Larry

EBEBRATT-Ed

You could raise the temperature of the water heater up to 140 and install a mixing valve at the water heater. If you store the hot water at 140 deg you will have more capacity. The mixing valve will provide 140 degree water.

It will cost energy $$$. The colder water in the winter does have a sizeable effect. Follow @Larry Weingarten suggestions first.