I have a 2003 John Deere 5520 cab tractor with less than 500 hours that I use a bucket and also forks on, but mostly forks. The tractor has recently developed an issue that is especially aggravating when using forks but occurs regardless of what implement is on the front. When I go to raise the forks, the whole assembly will drop from 6 - 10 inches before rising. If I try to tilt the forks back, they will tilt forward about 10 - 15 degrees before tilting back. As you can imagine this make it almost impossible to move pallets of material and can be dangerous. I've accidentally dumped several loads by accident. I have checked the hydraulic fluid and it is right on the full mark on the dipstick. Changing the filter didn't help. The rockshaft operates correctly and doesn't drop. All hydraulics operate at a reasonable speed, the drop on the front end is the only issue. I can leave the forks raised with a heavy load and there is no drop until I try to raise the load and then it will fall momentarily before starting to rise. It also doesn't matter how long the load has been on the forks - same results. Also, the problem exists in both hot and cold weather and regardless of whether the tractor was just started or has been running for hours and the tractor and hydraulics are thoroughly warmed up. Any ideas?