Was over at Deko's site today looking at the UP releases. I clicked on SD50 9843 to get a screenshot and noticed that the trailing unit looks to be UP B4282. I don't see this unit as part of the download list, so is it not yet available? Hmm...

That was included in the initial release as an AI loco, but it may have been dropped in the upgrade, as were the high speed units, in favor of the SD50s, GP15, and MP15s.

It is included in the version 2.0 set:




Note the prototype of this older locomotive is a 'B' booster unit, so is not modelled as player-driveable.