I have a pto wood chipper that I want to run off my F450. The chipper weighs about 900 pounds and the center of gravity is 6 ft from the center of the rear axle. I cannot get the chipper raised. Without the chipper attached, I can raise the hitch an additional 6 inches. (See photos) It has power steering and turning the front wheels full in either direction does not change the ability to lift.
I have been in to the system previously, had some problems but all seemed to be operating well, although I had not loaded the fast hitch until now.
https://forums.yesterdaystractors.com/viewtopic.php?t=1415433

So my question - am I looking at an issue with the priority/safety valve?

It should be able to lift it with no issues. Do you have any break aways on your tractor that you could put a gauge into? Any ag shop, farm, hyd shop, etc should be able to get you a 2000 psi gauge & fittings to plug into the tractor. That pump new should make close to 13 gpm & 1200 psi. The steering while being used will take 3 gpm leaving you with 10 to run other hyd functions in a perfect system. If knew the size of that cylinder, could figure out how it will lift. It would be nice to have a flow rater, but those things are expensive.

The picture I should have added

Again, my gratitude to you all.
The lifting points were lowered on the chipper and a chain used as top link. It does lift although it hesitated. I have it 7-8 inches above the floor. With a foot adjustment It will be 12 inches which is enough to move it around our parcel.

Thanks gentlemen. Mark, I believe that adapter is from a Woods. I picked up several years ago with an eye to finding a use in my F230. I do not have any Woods implements.
I am working on lowering the attachment points on the chipper.
The legs of the chipper will adjust 4 inches lower which was an initial goal.
The 3 point adapter height is at the chippers manufactured height. The rectangular tube lower down is my fabrication to attach my F230. I am going to pull the adapter, use the 450 points i have to lift from the rectangular tube.

I think, just like D slater you are starting off too high where your hitch is attached to your implement. Although I believe it should be able to lift where it is, IF it is 900#, even raising it only 6 more inches is really not high enough to move around like you would want. To prove that you need to start with a lower hitch position, back up onto some flat boards 6 or 8" high(something safe) and try to raise it. If it raises, you may want to re-engineer your hitch.
Is your 2 to 3pt adapter from a woods rotary mower? I have one like it. Mark

I would check the oil level before doing anything. Pumps on those tractors were known to leak oil past the seal when things got worn a bit.

Without a pressure check it's just guessing. Lifted round bales with center of gravity back that far with a 400 with same hitch heavy enough to back up a slight grade if wanting to keep front down with frame weights. So it should lift it. One thing that would help is to have the hitch point lower at lift end. Lift cylinder angle for most power is when top arms are below level. Higher they get the less leverage at lift arms.