Of all things in services that are random and/or unique, fuel is not one of them. That fact that every AC44 starts with 4450 gallons of fuel, GP38 with 1400, SD40 with 2900, Class 66 with 1,407.8 (and the others have no digital readout so I can't tell what they start at.) is not particularly immersive. For one thing, it seems odd that they all start at the same level, but it's not quite 100% full-it's just almost full. (Maybe to allow for refueling despite all of the fuel levels being the same?) And in real life, you are not going to see locomotives, not even in the same train (except maybe for DMUs) at the same fuel level at all, and rarely will that be almost full. Giving a bit of a random range to fuel levels in services (I would say down to no less than 30% or so, with around 70% being the most likely, but that depends on locomotive [big AC44s will rarely get super low on fuel]) would spice things up a bit and make services generally more believable and have a less structured feeling.