[MKS427]

You may be experiencing bump steer, which occurs if you have uneven steering geometry. Factory Five had this issue on earlier models, however I believe they eliminated it with a rack specifically designed for the car.
Contact Mike Forte, he may know or who would know how to fix your issue specific to a Backdraft.
Tramlining "wandering" is another condition which you may be experiencing. This would occur with an aggressive "racing" type alignment and wide tires.