Need help reading these plugs !!

Smooth to the touch it might be, but was there material worn away when the ringland broke. If you caught it early which you seem to be in touch with you truck you will likely be ok with a new slug in the hole.

On the other hand it could be smooth but no longer a truly round bore. Also smooth is a perception, not a measurement, it is also ones perception which leaves it open for interpretation. Smooth to a guy with calloused hands???

I think you need to see this for yourself if you feel qualified enough to judge the cylinder bores condition. If not you are going to have to go by what they tell you.

Also you need to try and figure out why you broke a ringland. It could be a freak situation, too rich or too lean. I do not have a huge depth of knowledge on the 4.0 but I would try and find out if cylinder 6 is typically over or under fueled, it could be a inherent design of the 4.0 since you mentioned it starts there at the cylinder first typically.