Front Suspension Lower Ball Joint problems of the 2000 Ford E-150

At 35,500 miles on my 2000 E-150 series van, the vehicle had a problem with pulling or "drifting hard" to the right. After requesting that the vehicle have a front end alignment check, the dealership found that the ball-joints were in need of replacement. Joints were replaced under manufacturers warranty on 07/2002, but alignment was charged to me. Now the vehicle was just in for the same problem with hard drift to right (at 55mph, the vehicle would make enough of drift to change one full lane in 5 seconds) was told by dealer that the ball joints were bad again, and were replaced under extended warranty plan. Was told by dealership that drifting was normal for vans.