Hi,
For starters, OTM deals with "assets/trucks" via the single shipment - single equipment model. This means that 1 shipment represents 1 truck move. So for round trip milk runs, there will be 1 shipment for every move.
We also find ourselves wanting to use OTM for the functionality mentioned above. However, 5.5 does not really manage trucks and drivers in the manner that would be helpful to operations. Hence, we are considering to build our own custom extensions to OTM that will keep track of the trucks and deliveries and send it to OTM for rating and financials.
I have not seen the asset functionality in 6.0 and frankly the literature and slides do not communicate much - only one line functionality that may meet or totally miss your expectations.
I am looking forward to 6.0 but until I see and understand the actual functionality, I am not holding my breath
Hope this helps!