Printing to transparencies via NT server

We have a few users printing to tranparencies from NT workstations to laserjet printers connected to Jetdirect boxes on an NT server. Everything prints as normal on A4 paper etc, but we continually get users complaining that the transparency printing is faint!! The print queues are configured correctly with NT Forms set to transparency for trays 2 on all printers but deskside insist this is a server issue. NB: All queues are using the latest drivers.