I tried thick, cotton, heavy matte and heavy gloss but the results are always the same.
Does the paper actually go through the printer slower when you change the settings? If not, it's probably ignoring the setting. When mine does linen stock the paper travel slows down dramatically.
You can try other software (Photoshop in particular seems to gleefully ignore any printer-driver settings I throw at it, I guess Adobe obviously [thinks it] knows best) but you may be out of luck. Of course, "settings in drivers do absolutely nothing" is a failure, so you shouldn't feel too bad about contacting support over that.