When did you last change the Hydraulic oil and HST filter? What oil did you use.? Something wrong with this picture. Shouldnt be any issue at that temp. Hydraulics and HST is on separate filter. I am thinking maybe the filter is plugged OR the oil is too thick. Perhaps you need to drain, flush, change all the filters and fill with SUDT2 , the full synthetic. It is supposed to flow better than the UDT or SUDT (I hear that SUDT is no longer stocked by dealers)