I had the same problem, and the same setup as you describe with your drag link. Whenever I would hit a bump, the truck would jerk to the left and then back to the right as the suspension compressed/ extended. The steering wheel wouldn't be affected by the bump steer. From what I could understand from all of the techincal info on the internet, The drag link must be paralel to the ground, and a longer drag link has less bump steer than a short drag link. I had the drag link adjusted to be much closer to level and wow! what a difference! It took out at least 80% of the bump steer. It takes a pretty big bump to feel any jerking at all now. Cornering on the highway is better now too; bump steer tries to steer you to the outside of a corner as the truck leans and compresses the suspension on one side.
I also installed a front sway bar to help on the cornering.
Hope this helps.
