I've also had problems with THICK card stock and duplexers. On my ancient HP Laserjet 4100 and 4050 laser printers, the duplexer can be slid out, and somewhere I have the plastic bits that the duplexer replaced. Fewer twisty paths, fewer jams.
KIng Beowulf is correct about twisty paths. At some point, the path leads to Kinkos. I joke that my HP4 can print on anything (T-shirts? Sandpaper? Plywood?), but I will probably need to tear down and clean the machine if I actually tried those materials. Note that tearing down and cleaning should occur after tens of thousands of prints. At least, unplug, pull out the trays and toner and normally removable bits, and suck with a powerful shop vac. Or buy much better paper than Office Depot Redbox. Tektronix used to make printers, then sold that division to Xerox. Some Tek printer adepts still live in Oregon. They should be answering this question. Better still, HP printer adepts in Corvallis. BTW; when Tek closed shop, I purchased a few boxes of A4 "square root 2 metric" paper (Europe, Japan, China, etc), which I still use to print foreign technical papers. I'm about to use the last reams. Amazon sells A4, Office Depot and Kelly Spicers do not. Good luck with your printer; them file cabinets ain't a gonna fill by themselves. Keith L.
