You do have the lift arms adjusted level when using the disk, right? Sometimes when using the plow you have to shorten the right-side so that the plow is level when the tractor wheel is in the furrow. When done with the plowing you have to remember to put the lift arms back to level for the other implements.
If all implements are pulling to the left I would check everything on the tractor carefully, that no part of the linkages are bent or installed wrong, both lift arms are doing their share of lifting, etc.
I'm not familiar with your particular JD, but a lot of tractors allow you to move some pins in the lift arms so that the lift arm can either float or be fixed. I would set them to the fixed postion, no floating, and be sure both side are set the same. If there are multiple fixed holes be sure both sides are set the same. I've also seen tractors where the draft sensing mechanism is on the lower links and you can actually attach the lower lift arms to different points so as to vary the draft sensitivity. Again, if you have this be sure both sides are set the same