I'm not sure it's a gearing issue. Sounds to me like a tweak issue. I'd check steering trim. Toe-in symmetry. Suspension symmetry. Check the driveline to see if one wheel is binding.
OH, and BTW, what car is it? Belt or shaft? Do you usually roll into the throttle? I ask because if you clamp the throttle, does it pull left in 1st also? I'd check the chassis setup. It could be one of a million different things.