Is this WH a standard model with non-simultaneous operation? The nameplate will say “top 5500, lower 5500, total 5500”. If it is built for simultaneous operation the total would be 11,000 watts. What is the wire size on this circuit? What is the breaker size?
A 5500 watt element can make about 25 gallons/hour of 90 Fahrenheit water rise water. Also, inlet temperature can greatly affect recovery; It takes a lot longer to heat water from 40 to 140 in the winter than from 70 to 140 in the summer.
If this is a non-simultaneous WH on a 30 amp circuit and #10 AWG wire, can you get another circuit pulled to it? You could change out the lower thermostat with another upper thermostat and wire the WH for simultaneous operation. This would give you an 11,000 watt WH making 50 gph. Either element can operate as needed.
If you are willing to do this don’t forget change the anode rod.