I have a 12 gallon gas/electric Suburban water heater.  It works fine on gas, but on electric it doesn't heat the water as hot as I would like or as hot as it used to.  I changed the heating element but that didn't help.  I understand the thermostat for electric is not the same as the thermostat for gas.  Is the thermostat adjustable?  Would replacing the thermostat solve the problem?  Or could there be something else?

Thanks.

The thermostat is not adjustable but I believe an adjustable one is available. To be sure if it is used for both heat sources I need the Suburban model number. 
 

You can go to Bryant RV website and get a copy of the service manual. 

Check your electrical connections.  Ours wasn’t heating as hot, then wasn’t heating at all because of lost connection.  Everything reconnected and tightened, back to normal.

When was the last time you flushed out your tank? Mineral deposits develope and fall to the bottom of the tank, impeding heat transfer. I flush our tank out semiannually.