Yes, you will not be able to rev the car in park or neutral past somewhere in the 3500-4k range due to the rev limiter on all Grand Prixs of this era. I am stumped on why the radiator cracks but I would get a new radiator cap and double check the hose that goes to the coolant overflow tank for obstruction. What type of coolant are you using now? Did you purge the system of air first before driving it after replacing the radiator and the thermostat?