Use of HP UPD is in my experience counter productive.

If you need to print to HP use the CLJ 9500MFP PS driver (or PCL6 or PCL5c if you must).
This driver works on HP LaserJets.
This driver is cluster compliant comes in 64bit and 32bit flavours and works with Novell/Iprint Citrix – the lot.

Some care needs to be taken with configuration to ensure best performance.
– Within advanced disabled “advanced features”
– Ensure font substitution is set to “down load soft font”
– Set print processor to “winprint” & “raw”
– Stop PDF pass thru
– Stop PDF error handler

Although this driver only supports 4 trays max it will work with any number of trays, just use paper type when sending job.

If this does not work for you, or you want to print faster use Adobe’s Universal Print Driver – it’s easy to modify the PPD to add duplex and colour – it took me about 30 mins to sort and test.

– wapicho commenting on I’m not the only one annoyed with HP’s UPD print driver.

Use of any Universal Print Printer is counter productive, is what I think too.
I’ve discussed before why printer vendors like to use UPDs (hint: they’re a pack of cheap bastards), and why I loath them.

Wapicho’s advice is good, and should work very well.  Particularly with Citrix environments, which can be fussy.

Reminds me what I used to do in the past to get troublesome laser printers to work.  Use the HP LaserJet 4 driver.
The HP LaserJet 4 Postscript driver is a handy “works with almost everything” driver, particularly Citrix.  But it has it’s limitations (lack of more than 2 trays, for example).

In the far far past, LaserJet 2 drivers were a good substitute for just about any Postscript printer.