Where it is only pdf, it isn't likely the driver, more likely the files, I will assume they are being made in-house, so.
If you get slow prints try enabling/disabling Print as image
If it works better with that enabled, the file is clearly the issue, it should be flattened, it should have the fonts properly embedded, and if you are making them, you should be using PDF/X instead, as it will fix those problems for you.
It could also be a file size issue, you are overflowing the buffer, which happens mostly when people drag and drop content into the file and then create the PDF, which means while the pdf displays as 72 DPI (They all do) pictures in it can be anything, like a 22 MegaPixel goliath from a DSLR. In which case the printer has to do the conversion to whatever the output is (Typically about 300DPI). That takes a lot of power to do, more than a printer has. If you import the file into Indesign/Word etc instead of drag and drop, it negates this issue by formatting it properly during the design process.