Are you sure? When I just look at the model number, instead of the serial number, they all have high flow hydraulics.
Try just entering in "T590" under the MODEL NUMBER tab and then look for the tab that is closest to your serial number and see if this make a difference. Also try different search words. Try just entering "high" in the search.
If you want to give me your serial number, or the range that it is in, I can help look.
I know that on newer Bobcats they started using the computer to lock out certain features of the machines. So say you did not want the high flow option, the dealer can lock it with the computer so it doesn't work and you pay less for the machine. Then if you decide later that you want high flow the dealer can turn it on for a price. Who knows what type of weird codes this could cause. I would not think that this would make a difference in the parts catalog when entering in the serial number though.
Hope this helps