Thank you very much to all for the helpful responses!!
Apparently, we resolved the issues by doing the following:
1. The stop bolts were installed on the back.
2. Drag link and tie rods were installed properly.
3. We reduced the free play of the steering wheel shaft.
4. The kingpin bearings were installed properly.
The only issue is that the shackles are too open with the wheels on the floor.
I was told it is because the main leaf spring is too long. Please provide the original main leaf dimensions as well as for the second leaf.