According to my research i can get by with an 06 impala hood lift rod support.
Grand prix specs are
Extended length 21.74 inches
pounds of force 99
shaft diameter 6mm
body diameter 15mm
Impala specs are
Extended length 21.12 inches
pounds of force 112
shaft diameter 8mm
body diameter 18mm
They are both 8mm ball socket connection.
I really see no problem in going to this other rod if it fits. It might only open .5 inches lower than stock but the impala single rod opens up my girlfriends hood just fine and it only uses one and the hood is metal. Mine is fiberglass. There is a chance that maybe all i need is a new hood prop that has all the juice in it to handle it .