lift and steering

[red450ih]

A friend has two trucks (73-87) that have 4'' lifts and I was thinking about doing the same to my trucks until I drove both of his trucks last night. When you hit a bump in the road the steering wheel turns back and forth until you get passed the bump. He said he has gotten used to it, but I don't think I could. He has added all new shocks, tire rod ends and ball joints, not to metion the correct steering arm for the 4" lift on both trucks. Any suggestions on how to correct this?

Thanks,
Keith