Suburban hot water heater luke warm problem solved

One of the 'classic' way for luke warm water be it Suburban or Atwood

Inside/outside shower turned off via button on shower handle.
Yep...faucet then becomes a mixing chamber and Cold/Hot mix resulting in 'Warm" water

Anther way is the Water Heater 'Bypass' being left open


And then there is the Atwood XT model with 'Mixing Valve'....Hot from tank to mixing valve gets clogged up and then Cold just flows.