I recently had an oil leak on my Kubota B7100 and it was not fixed right away. After fixing the leak and refilling the hydraulic oil, I noticed that the reverse gear is slow. It also goes downhill in the forward direction. So I changed the hydraulic oil filter and refilled the hydraulic oil. My problem still exists.
Have you used the correct grade hydraulic oil? Incorrect viscosity can cause the problems you describe. Clean the hydraulic line filter. It is a good idea to clean the strainer every time you change the filters. The hydraulic transmission usually has a filter separate from the hydraulic system. Are you sure you have changed the transmission filter? Cycling the steering a couple of times will normally bleed air from the system.