It could be possible that the old (new) king pins have worn out prematurely. I recently greased my new king pins for the first time before putting the truck on the road for the first time as well. What I discovered is that the kingpins did not want to take the grease. The grease made it to the first joint and oozed out. So, I am concerned that all moving interfaces do not have adequate grease. My plan is to keep applying grease after every few hours of operation to ensure the grease slowly works it's way to where it needs to be. Assembly grease should protect the bushing and kingpin for the first few hours of operation ... I hope.

Just food for thought.