Same here, did it first time, didn't know it was an issue.
Wouldn't surprise me if it's one of those framerate bugs that crops up in GTA games (e.g. in SA, there's a mission where you have to ride a motorbike up a ramp on a plane that's taking off - I found it impossible until I turned the framelimiter on. Likewise in GTA3 I found some vehicles went very slowly in reverse with a very high framerate).