They are the same company. I used to work for them as a driver and I was doing work for both but only getting one pay packet. I would put in one pay sheet and they would work out what was NZC and what was posthaste (different pay rates) then I would get the one deposit in my account each month.
Also all of their trucks share their loads and a lot of the time you get an NZC truck towing a PH trailer or the other way around