Steering problems on lifted 72 Jimmy

[RShaips]

I put a used lift kit from another Jimmy that I bought onto mine. The front is a 6" spring lift with a steering drop and the back I believe is new stock springs with a 4" block, the back is about 1" lower than the front. I am going to replace the back with 6" springs soon. Anyway I also put 35" tires on it at the same time. It steers terrible, it is all over the road. I have adjusted the steering box and checked my steering stabalizer and everything is good. I took it to the shop and had it aligned and they said that they could not get the caster set right without shimming the springs or ball joints. Said it was 4 degrees out,top of front axle needed to be tilted back 4 degrees and that this was my steering problem. I have had a lot of lifted trucks over the past 30 years and have never had a problem like this. What's the deal? Thanks