I have an 80 gal State Select Elect Hot water heater. After two showers the hot water runs out. The water pressure is 85 lbs. This has been a problem for quite some time. What is the most likely problem and how do I fix it?

Probably one of your heating elements are burned out.

Turn up a little on the temperature controler on the Water heater or don't use too much of the hot water.
That happends all the time when the hot water is over use. Same for me, when my wife and kids done taking a shower, all the hot water are gone and only warm water, but it takes a while to get the hot water back :)

You could have a broken dip tube in the heater. Do a Google on broken dip tubes

jehoward - THE thermostat can be the trouble or it very well be the ( ANODE ROD) :: This is missed a lot of the time on repairing the hot water tank :: ANSWER - IN a area where the water has a lot of minrails in the water ,this rod will either rot off up close to the top in the still cool or cold water level. This rod unscrews out to be replaced or checked ;; NOTE- ( TURN OFF POWER TO THE TANK >DRAIN OFF SOME OF THE WATER <AND RELEASE PRESSURE:: DISCONNECT THE HOT WATER LINE ON TOP OF TANK< ::NOW UNSCREW THE ANODE ROD OUT OF THE TANK : THIS ROD IS NORMALLY LONG TO ALMOST REACH THE BOTTOM OF THE TANK.
IF THE ROD IS BROKE OFF OR ROTTED OFF <THEN REPLACE WITH A NEW ROD< IF IT IS THE THERMOSTAT THEN YOU WILL HAVE TO DO A LITTLE MORE TESTING TO FIND OUT WHICH ONE IS BAD :: FIRST TRY THIS :: IF
YOU FIND THE ROD IN GOOD CONDITION THEN, JUST COME BACK ON THIS POST AND HOLLER AND I OR ONE OF US WILL COME AND TRY TO HELP YOU OUUT ANOTHER WAY ::GOOD LUCK AND HAVE A GOOD DAY:: F.B.E.