It's because it has four gears and the car was built in the 70's, when american cars barely went over 100 mph.
American cars had a ~120mph limiter no?
I just bought a premium 1970 dodge challenger and it doesnt go over 115 mph, i tried it stock, with engine upgrades, took off traction control, manual and automatic transmission, different tracks, and it doesnt pass 115 mph, it makes no sense. It's a 430 hp car...
The FC transmission doesn't whine as much with update 1.06. At least, That's what I've noticed.