The partial print problem and slow print problem with our hp designjet 750c has been fixed by having a new faster, with larger memory capacity pc serving as print server.
HP 750c doesn't have enough built-in RAM to handle some of large VW files. There was an option of upgrading our printer with larger RAM but having a print server with faster processing chip and larger RAM was much cheaper option for us at the end.
We now have all our printers (hp designjet 750c, epson stylus photo 3000, epson stylus photo 1290 and brother fax/laser printer) connected to this print server pc that handles all the print queues.
We haven't had much print issues since then