I've been dealing with a persistent issue with the FMX in my '69 Mach 1. Unless the car is up to operating temperature, it absolutely will not start out in 1st gear. It will stay in 2nd taking off, and only by manually shifting or flooring the accelerator will it downshift into 1st. It's really aggravating, to say the least, and I've heard that it's rough on a transmission to make it pull like that. Once the car reaches operating temperature, it's fine, and from a dead stop it starts out in 1st gear as it should.
I've always heard that FMX transmissions are notorious for this problem. This one was professionally built and has very few miles on it, and it's done this since the day I brought it home from the transmission shop.
What causes this, and is there any way to fix this problem?