Uninstall current Laserject drive and install new driver

Side note:  Remove any "support" software that HP supplied with the printer using Revo Uninstaller.

HP's uninstalls are not clean; they leave keys all over the Registry.  I did a manual cleanup of the Registry once after uninstalling an HP printer and there were over 1200 keys left after doing the Uninstall using Revo.

So if there's a corruption that requires reloading the driver there's no guarantee that loading a fresh copy of the driver will solve the problem due to all the "stuff" left.  Therefore, be aware going in that this may not solve the issue and do a full backup of the system before attempting anything.  Then no matter what happens you can get back to the way things are now instead of having to deal with yet more nebulous issues.

John: HP instructions talking about removing the printer USB connection before uninstalling, installing. But the sequence is not clear. Or should I simply follow your instructions without disconnecting? Also I can use Revo to clean up leftover registry entries. (Yes I have a registry backup utility.)

Got it. I'll post with results.

If you have a 64 bit OS, revo uninstaller free will not uninstall any 64 bit apps.  You need the pay version for that.  Or, you can use IObit uninstaller portable, its free and it gets both 64 bit and 32 bit apps along with other stuff like Windows 10 apps and browser toolbars and addons.   The portable version does not have the nags that the installed version from IObit includes.

See:  https://portableapps.com/apps/utilities/iobit_uninstaller_portable

Got the paid version. Thanks.

Is the whole setup corrupted or do you just want to move to a new driver?
You can simply replace the driver alone by opening Devices and Printers
Right-clicking on the LaserJet's icon and choosing Printer Properties then in the Advanced Tab click New Driver ... to launch the
Add Printer Driver Wizard, use the 'Have Disk' option to point Windows at the unpacked new driver files.

Hm. I'll try that first thing in the AM. Problem is on wife's win7/64 machine and she'll be in her city office tomorrow so I can troubleshoot her home machine. Now the printer works fine when printing a single page. No extra blank page. But when I try to duplex on that machine, it spits out an extra blank page. Cannot find a simple solution, which is why I thought I should try a new driver.

I would be careful about using Revo Uninstaller. I have had it prevent subsequent reinstalls of the same software. Try the plain driver uninstall / restart / reinstall steps.

>> ... Printer keeps losing its duplexing and prints an extra blank page ...

Are you (re-)installing a driver just because the Print dialogue no longer offers you the automatic duplex option?

If so, note that the 'automatic discovery' feature used by some drivers on installation (or update) doesn't always work, so all that might be needed is to notify the existing driver of the presence of the feature.
i.e. ensure that the driver knows that a duplex unit is present on the printer (assuming that one is present):
 

You'll probably need to be logged in with administrator credentials in order to change the device settings.

Not quite sure where the "extra blank page" fits in, unless it is the (intentionally blank) rear face of a duplex page.

I wanted to let the machine run a few days before I reported back. It turned out that the toner cartridge was not fully seated in the chamber. I had pulled it to make sure the metal contacts were clear. Wiped them with a tissue (to absorb any finger oil), then sprayed with air, then when I went to put the cartridge back, I noticed that it needed a bit of an extra push to get it fully seated. A real rookie mistake - should have checked all cables and moveable parts first. Been three days and it's duplexing without the extra page now. BUT...I'm very glad to have all the suggestions handy. I wasn't sure about the uninstall/install sequence. Now I am. And perhaps someone else will benefit from the exchange: John's caution about Revo is well taken. I too have had it wipe out critical registry entries. Sometimes, however, you have to use it. I tried to uninstall an older version of AcronisTI using the regular install and all of a sudden my USB ports were disabled. Revo caught the three acronis drivers that had been left behind and were causing the problem. But it's a risk to use that program on software like HP when you have other HP hardware (like a scanner) on the same system with an HP printer.

Thanks for the update and I was happy to help.

Corrigenda:  Printer started printing an extra page again with intermittent duplexing. I knew it couldn't something as simple as re-seating the cartridge. So I'm about to uninstall/install.

Tried three times to uninstall/install and the same thing is happening - a blank page with every run, single-sided or duplex, actually a blank page after every page.

Is there any chance trying a different printer, OR, this document on a different computer with different printer. There may be a hardware issue still on this printer.