I had fun with this game - thank you for putting it out there.
If you're interested in doing updates, I found that by the time you've 'doubled' vehicle capacity three times, each truck can carry more than the total storage capacity for undelivered milk. There's no reason to unlock anything past that point, since every truck will always consume the total sum of all the player's milk of a given type - this makes the 'triple capacity' upgrade irrelevant, as is the last two 'double' options. From the phrasing, I think you meant to have each upgrade purchasable once? That would make more sense re truck vs silo storage sizes.
The automated truckers don't seem to care about capacity upgrades, delivering odd and low quantities of milk. 88 milk in a run with a tanker of 400 units storage, for example.