For your graphics card driver I would go to Nvidia's website.  From the drop down menu select GeForce, GeForce 700 series, GTX 745.  This should be the correct driver for your video card.  After you do a new install, if you update Windows, it should update a lot of drivers for you.  I would backup your computer to an external HD before doing anything.  If all else fails, you can clone your present HD to the new one using Macrium Reflect.  

Thank you metamorphosis for your comments.

If I upgraded the card myself, then I would go to Nvidia's website. However, for an OEM card, I prefer to use Dell's site as they are more apt to have checked compatibility issues. And they do seem to have the correct driver. I'm just baffled that it doesn't show up under my build. Dell should do a better job with this. They have a great tool to list the drivers specific to each build, but it doesn't seem to be accurate. I also realize that Windows will install most of the drivers. It's the other ones I'm trying to nail down before I do the clean install.  I'm also with you on the backup. In fact, I'm going to keep the original 1TB HDD intact. I'm installing a 500GB Samsung EVO 850 m2 which I'll do the clean Win 10 install on. Then I'm adding a 3TB HDD and saving the original.

The 745 is just missing from the main descriptive heading and the Applies to section. A simple website mistake. I have notified them. The driver will work for the 745.

Mine shows the 745 as an available driver but the driver it supplies is not compatible with Windows 10.  It seems like the drivers listed for the XPS8900 aren't all Windows 10 compatible.

Mine initially showed the ATI also.  So far this computer has been a nightmare.

Well, after 40 minutes on tech support chat, Dell support just told me that the XPS 8900 doesn't support the Windows 10 drivers for the NVIDIA geforce 745 and I should revert to Windows 7.

Gee, I am glad that I did not know that the XPS 8900 does not support the GTX 745 under Windows 10, given that that is how i ordered and received my computer, and that it is working correctly.

According to the Device Manager's Display Adapter Properties Sheet for my GTX, I have the nVidia driver 10.18.13.5382, dated 07 Aug 2015, as well as Windows 10 Home, which was updated 10 May 2016.

Now that I have learned that this combination does not work...

This might make sense if the computers came with Win 7 and we upgraded to Win 10, but it doesn't make sense when almost all of the 8900s now come with Win 10, and most of those have the GTX 745. You can see from my post above that my computer has a GTX 745 driver installed. So, there obviously is one that works with Win 10. The problem is with identifying the correct one to use (if any) from the Dell site.

Thank you Chris.

It's been 14 days and the Dell site still doesn't list the GTX 745 in the descriptive heading.

What concerns me is that when you do a Dell site search for a GTX 745 driver, the one I listed above shows up. It states that it is for the 720, 730, 745 & 750. Was it also an oversight that these others weren't listed for the newer one? That doesn't seem likely.

I presented this problem to Dell tech support via a "chat" session. They have "elevated" the problem and promised an email answer. I will post the results.