electric hotwater heater trouble

I seem to be running out of hot water faster then i should. water always starts out to be hot but within 10 mins in the shower it starts to cool off quickly (didn't do this before) i have tried replacing both thermostats and both heating elemeants with no luck. any suggestions?

Did you look at the dip tube. It's on the cold water nipple going into the w/h. Pull it out and see if it's all there or if it's split. If it broke off at the inside top of the tank, I don't think you would get more than lukewarm water. I think you gotta look there.

how hard are these to replace?