So I went out and did a little checking on the tractor.... 
Hydraulic level okay before and after engine start. As soon as engine was running, I operated the three point several times, and it lifted &amp; lowered just fine, and fairly quickly at about two seconds when at 1400-1600 RPM. I then shut it down with the three point raised, and fluid level was still fine. Fluid level was full whether 3 pt. was raised or lowered, engine running or not. Lift time was only about a second or so at 1800-2000 RPM with the system still fairly cool. I took it out to the field, and worked it for about 45 minutes-1 hour. I noticed that once the hyd system was warmed up a little bit, the lift time was a little longer, about 2.5 seconds at 1400-1600 RPM, and two seconds at 1800-2000 RPM. Once it was fully warmed up, the 3 pt. didn't want to lift much at all; only the front of the brush hog mower was lifting a bit, as the wheel in back stayed on the ground. If I backed the tractor/mower up until the back wheel was on higher ground, such as the driveway, it would then seem to hold it that way, at least for awhile. I could also physically lift the brush hog while the hyd syst was trying to do it, with the same effect. -It would go up, but I was lifting pretty hard to get it to raise. Higher engine RPM's tend to make it want to lift better, too, but it used to lift well even if engine was running at slower speeds.
When I shut it down, I left the 3pt/mower raised, when I went back out after about an hour or so, it was down on the ground -but I think that's normal? 
If  I work it hard for awhile, such as PTO or high RPM work in general, hyd fluid looks a little foamy/bubbly, but then it always has, and looks better after shut down for awhile.
Would a heavier oil work better in the hyd system than the John Deere Hygard? How about 30 weight engine oil? I was told to use Hygard, as it is more resistant to foaming and was better in general.
Do you think when I started to go up the steep hill, that maybe too much of a lifting angle ocurred, and put the draft control out of adjustment? I had also hit a large, embedded rock with the brush hog only, causing it to lift rapidly in the air, then come down fairly hard. The blades never hit the rock, just the mower deck. It seems like these two incidents, very close together, might have put the draft control out of adjustment. 
Is there a easy way to check this? Would the high lifting angle events I described cause the draft control to be out of adjustment anyway?
The top hole of the three on the lift rocker was broken off on one side, and cracked on the other when I bought this tractor &amp; brush hog together. The seller had the three pt. hooked into the middle hole, and it has always stayed there.