I found the problem. I followed tdurrett's suggestions and found that I don't have any of the files that "shelbysounds.aud" calls for. I replaced the file with the mustang one so now my shelby has a mustang engine, but it works. I will do the same with the AC Shelby cobra, since it uses the same "shelbysounds.aud" file. If you could send me the files that go with "shelbysounds.aud" I would very much appreciate it. I assume they go in the */GTL/gamedata/sounds/cars folder.
Thanks again for all the help