Jimmy, Let me start by saying I am rusty because I have not owned an electric heater in many years. Maybe this feeble bit of info will help. I believe a lot of water heaters use two 4500 watt elements but only energize one element at a time. If you measure voltage across the screws, you will only get voltage when the thermostat is attempting to deliver energy to the element. So you likely won't get voltage on both elements at the same time.
There's a couple of ways to check an element. If you remove the wires going from the thermostat to the element, you can put your multimeter on continuity setting and should get a "beep" if the element is probably good. If you have a "clamp around" meter, you could check for amperage running through the wires while the thermostat is delivering power. Significant amperage ( 15 amps or so) would indicate that the element is likely functional.
Basically, it's got to be one of two elements or the thermostat.
Other possibilities include you put on a new showerhead with much higher flow or you're taking too much time in there spanking the monkey.
