reproduce:
use GMC as towtruck - tow another GMC - go throug tunnel from smithville dam to drummond island
result:
both trucks are at same place - start driving with towtruck - connect winch to second GMC drive to bridge.
unload second truck (the pulled one) - you cant switch to the empty truck.
not via map - not via change truck - not even after going to smithvill dams garage.