I've been working on it and it's really frustrating. From what I can give you, you can either drive the porsche gt3, lancia stratos, or wrc stratos but only one of them for a game save. The only way I can stop it from freezing is:
1. Have it as the first car in your garage.
2. In Arcade Mode, you can drive it in the races, but not in the time trial.
3. In Simulation Mode, it is the only car you can ever drive, and you can't enter your garage.
So, I think I'll stop pursuing GT3, it seems to be too smart for me

.
If you want to figure it out yourself, do what I did: get a sharkport and download it here.
http://www.geocities.com/sypto1974/index.html
Mess around with this program and work with the "Change Car" list and you may be able you get through this really annoying bug.
If anyone gets a way to have all cars on one save, make sure to announce it! I'm stuck and I'll just stay with hybriding...

(At least for now

)