Truck Com is the BT / Toyota software.

BT / Toyota have in the past allowed certain customer's technician's to have a licenced copy & the connector leads.

Depending on the truck in question, the basic Truck Com functions are:

Download software update's to the electronic unit's.
Copy parameter's so you can deploy them across a fleet of the same spec truck.
Generate a truck report for BT technical service's to view.
Update hour meter's.
Change factory parameter's ( Can key cant do this! )
Erase the error log.

Truck Com has other diagnostic function's as well but on a RRE you can get these up on the CID display with the can key.

Also your lowering parameter 342 need's the RRE to be switched OFF else it wont let you change it.

You would need to ask your BT / Toyota dealer for Truck Com & licence key.

Truck Com, can key & RRE training, ask your BT / Toyota dealer nicely.