I have Gerber in my home (UNDER DURESS) as they WERE CHEAP and available at the time.
I would have rather bought a Crane toilet (less money BETTER PRODUCT)
Gerber as bad As I feel it is STILL much better than the NEW Kohler Or American Standard IMHO.
Are these toilets tank and bowl or flushometers?
Mine are flushometers and using the Sloan Royal are the only way to go. If you have the tank type you can try raising the water level to maximum (about a 1/2″ below the over flow tube) and adjusting the tank bulb according for a longer flush. Good luck