The 755 I had (although I've heard later models had discontinued this feature) did not need the parking brake to be set to get off the tractor. This was really appreciated on flat ground, where you could jump off and do something and then get back on. If the ground sloped, the tractor would creep a bit, so if that was too much, you would set the parking brake. How badly is your 755 creeping?
Yes mine is the older model that you can get off the tractor and it will still run. The creep is slow but you have to keep applying reverse when using the front end loader. I think there has to be a adjustment to keep tractor in neutral when forward motion is not wanted
The eccentric cam that Mechanos1 speaks of is located under right side step. You reach through a hole in the frame with a 13mm socket and loosen bolt#17. Then reach up behind the frame with I think a 24mm wrench and turn eccentric cam #18 until the creep stops. You should have tractor jacked up and safely supported before attempting this. Have tractor running with park brake off while adjusting. Tighten down #17 bolt to lock adjustment in place.