Caterpillar DP70 hard steering problem

Hi, We have a Dp70 and when the steering started malfunctioning ( hard steering and some form of kicks in the steering when turning) we found that the hydraulic oil was in very bad condition due to poor maintenance and that the return oil filter was exploded apart. We than change the hydraulic oil, suction strainer and return filter, whe took the flow divider relief valve and the overload relief valve apart to clean them. Because the bad steering problem was persisting we changed the hydraulic pump assembly ( charge pump and main pump), the flow divider relief valve, the overload relief valve and the obitrol (metering pump). After all that the bad steering problem is persisting again , when we jack the lift truck ( no weight on the wheels) the steering action is great and smooth but when you turn the steering with the weight of the truck on the rear wheels and the truck is not in movement ( simulating a tight space wide turn) when the wheels reach a certain travel angle the steering become very hard and slow to turn. We have no shop manuals or pressure testing gauge at our shop so we are left with no clues... Does a new relief valve comes with a preset adjusment or maybe it would be a good idea to crank to opening pressure of the flow divider relief valve ( without pressure gauge ....... ) bye turning 1/8 of a turn or something like that? thanks Waiting for you suggestions