Resource question = Unit 1/d, budgeted 8 units AC=8, working all 5 days, my p6 histogram chart says 4 for the week? how?

'day' has no fixed meaning in P6. All data is stored in hours, and all calculations are done in hours. Both resource units and durations.

Try going into Edit User Preferences  and changing the duration unit to hours

Also set the histogam increment to hours, then days, so you can understand the 'real' figures

It been a while since I set up resources, but in user preferences there is a setting for "Time Distributed Data" and you can pick day.  I also recall there is somewhere on the charts where you can divide by for example 8.  Personnally I can visualize 10 workers for 8 days, than 640 hours spread over 8 days.  I wonder what is most common.  Personally I would like to see a manpower loading chart - but think this works better in excell than p6, but than also quantity / production rate - but generally just use the udf for these.  I think most people know it is easier to do cost as a resource, but it complicates it if you also have resources.