I found out the hardway, before I even got home that the transmission oil is not necessarily suitable for US use. Some units in Iraq or Afganastan apparently put 15W40 oil in that big Allison for desert use and it will kill the transmission in cold weather. $75 worth of transmission fluit is a lot cheaper than $500 to $700 for a pull-out transmission.
When I had to replace mine, I talked to an engineer at Allison. They used to endorse GM products because of a corporate relationship, but he told me that any quality Transmission Fluid is okay. Mine blew out the low gear pack in -20 degree weather after 1800 miles of driving and 16 miles from its parking spot. If it had broken down a hundred miles earlier, I would have sold it on the spot for scrap.
The good lord only knows what they put in engines and differentials!