try custom page and there ought to be a setting in your printer driver
to affect rotation.

but if Tabloid works, what's the issue?

try seeing if your printer profile has a ledger setting. This is 11x17 as a
portrait instead of a landscape.
Also, your rip might be automatically set up to rotate all the pages in a
job to output in a certain way. one way to get around this is to make a pdf
file, rotate it there to match the side that you want as the gripper and then
send the pdf file to the rip. experiment with rotating the pdf file until the
rip gives you what you want.