Water Heater barely warm water - NO bypass valve

Late model Suburbans have the orifice built in to the burner tube. 45-60 minutes is not at all out of line- there are 50 pounds of water in the heater, the burner is 12,000 btu/hr, 1 btu raises the temperature of 1 pound of water 1 degree. A lot depends on the temperature of the incoming water. For the initial run, you are also heating the tank itself= more time. Once hot, recovery will be quicker.

Someone who still remember high school math can do the calculations. :)