The GAC is typically thought of only for people with disabilities...permanent disabilities, but it's available for anyone that can demonstrate a need. I'm gonna guess that you'll limp up that wheelchair ramp into City Hall and limp back out with a way to make your trip that much better. Good luck to you!
Keep in mind if the walking gets to be too much, there is always the rental of a
ECV. Not cheap but better than days of pain. While regular walking may not be a problem in everyday life...remember that you will rack up the miles quickly in Disney. If you need it, it's worth the money!
Jack...if you've never had an injured knee you simply can't realize that just stepping up onto a curb can cause a jolt of pain....whereas stairs can bring tears to a football player! And it's amazing how many stairs there actually are...when you're able bodied you don't notice a couple steps here and there, but OP will. Because of the ADA laws there has to be a way into any ride for wheelchairs, so all OP will get is access to these ramps, elevators, etc...a GAC is not a free FP or front of the line pass. Just easier access. Those actually IN a wheelchair don't need one because their need is obvious to every CM in the park...but when your injury is such that a glance doesn't show it, having the GAC means not having to explain it a dozen times. That's why Disney has it available, so that their guests can get the help they need without having to repeatedly explain it when it's not obvious to the world. Sadly it's also why some people make rude comments when they see someone else get to take the elevator or be escorted through a different entrance....their lack of full knowledge makes them misjudge folks. There is also a heavy misconception that a GAC is a front of the line pass because folks see them escorted away and they never are seen again, so the assumption is they're on the ride already and you're standing in line still...but it's not the case...there is a waiting area for the wheelchair and mobility impaired and they wait in line just as long before getting on the ride. Think about it....sometimes don't you come up to the front of the line and suddenly a car goes by that is already loaded and you think "how'd they get there? They weren't in line in front of me." Those are the folks from the wheelchair area.
Anyway...OP enjoy your visit!