4wd K5 steering issue

[72K5er]

I just finished rebuilding my K5. I replaced everything on the front axle, ball joints, tie rod and ends, rag joint, steering column, everything. The problem I am having is that the steering won't return to center after coming out of a turn. I have checked everything and it is good. I am running Offroad Design HD front shackles which are1/2" longer than stock. Is that 1/2" enough to throw the caster off and cause this? I read that these shackles are the same length that chevy started using in 88'. The steering is smooth with no play, it is just the return. There is a shim installed between the front axle and leaf to try to compensate. Could this be adding too much caster in the other direction? I believe it is a 6 degree shim. Any advice is greatly appreciated. Should I remove the shim and just run the shackles? I just want my steering to return. Thanks