hills = running up and down them, and not sideways on them.
check your owners manual / operators manual, you should be able to fill rear tires with a fluid, and sometimes recommend filling front tires with a fluid as well. (it depends manufacture to manfacture, including model to model, if it is recommended to fill front and rear tires with a fluid. fluid filled tires help lower COG (center of gravity)
backhoe when in raised locked transport position raises COG (center of gravity), remove it if you do not need it, and fill rear tires with a fluid, and/or get a 3pt hitch ballast box on.
slower = better / safer within reason
faster you go more likely a bump,rut, etc.. can cause machine to roll over. soft wet ground can give way quickly and cause a roll over.