I have a rebuilt C-6 I took out of a 77 F350 that when cold will start out in second and the when warn wants to start out in third,it will manually up and downshift fine but not automaticly. The only thing I have done to the trans since removal from the donor truck is change the fluid and add a Lokar shifter,I puut in type f fluid but since it was rebuilt should I have put in dextron. Jeff