My 65 when the engine is started the steering wheel turns hard right. If the weight is off the front end it spins right over, if the car is on the floor it tries to turn. When cruising it tries to steer right and will if the wheel is released. I have a new pump on the car (the old one did the same, but leaked) I have rebuilt the suspension and have aligned the front end. The shop manuel has nothing in the troubleshooting guide, and the locals scratch thier heads.

Your problem is no doubt in the gear itself.
You may have to pull it and go through it our opt for a rebuilt.

I just did this exact operation and can provide some pictures if you wish. However on my '64 I had to unbolt a cross member, unbolt the tranny, jack the engine up and all sorts of other inconveniences. The book has 5 steps, like hell you'll drop it out without doing anything else to help it out. HOWEVER this is for a '64. The boxes on the '65s are different as the '64 system was only used for one year. Let me know if you need some technical assistance.