I recently received 4 of these cars, three with knuckle couplers, and one with Rapido's, which though larger, will work with MicroTrains couplers. The problem I have with all the cars is the wheels are extremely tight, and do not roll freely on my track. In fact, at a train show this past weekend, my loco could barely pull them. Has anyone had a similar experience, and/or come up with a fix for this problem  (short of replacing the trucks with MicroTrains units, which are not prototype for these cars).