Speratic Watrer Heat

[warrencm]

I just bought a house that is 9 - 10 years old. The hot water heater is a 60 gallon gas heater. I have noticed that in the mornings my showers are just warm but at night time they are scalding. I take a shower at 6:30 in the morning and my wife will take one at 5:30. She states that it is just luke warm when she takes one. I have not been able to find any kind of timer device for the heater (I don't think you can time a gas heater). Does anyone have any ideas as to what could be wrong with it. Do I need to replace a part or the whole water heater?