You might have a broken leaf in the spring pack, causing a bias to one side. I have never encountered what you are describing, but I always use a Panhard rod on an I beam or tube front axle. This keeps everything centered nicely, and prevents the horrible "shackle rock experience", which can cause an immediate change of underwear if it happens at speed. The way I do a panhard rod , I build a bracket off the underside of the driverside framerail just behind the front axle . I use urethane bushed rod ends on each end of the Panhard rod and run it parallel to and just behind the axle. The bracket at the other end gets bolted to the inside of the batwing on the passenger side.