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Mine had similar "problems" when I got it. The previous owner had wire tied the control down to keep the lift from creeping up on its own. Turned out the pump just wasn't setup for the right job. The pump can be set for all sorts of jobs so be sure that it is set up correctly for the job you need to do. There should be a decal on the battery box just above the pump that shows you how to set the pump up. The pump has four manual adjustment knobs. The most commonly used set up for me is the hold position setting. The lowest knob on the side of the pump is the drawbar adjustment ("A"). It is used for pulling plows and the like and gives traction control. Turn this knob all the way into the body detent locking the plate into position. The second knob is on top of the pump on the side linkages. This is the hold position adjustment ("B"). Turn it so that it locks the two plates together, allowing them to move as one. The third knob is also on top but on the front of the pump's hold position valve. This controls the delay lift ("C"). Turn it all the way out until it hits its stop. The last knob is on the front of the pump about half way down. It controls the rate of lift ("D"). Turning it all the way out gives you fast lift. All the way in is slow lift. (I have mine set about halfway.) Once you have the pump setup for the job you want to do, you need to adjust the linkages. (I'm going on memory here so hopefully someone will check me on this.) First with the tractor off move the lift control to the full up position. There is an adjustment just under the gas tank on the large linkage to the hydraulic pump. Loosen this and push the linkage down to take all the play out of the pump and retighten. Move the control back to the down position. Turn the second knob I mentioned above (the hold position knob "B") into the detent in the body of the pump separating the two plates and locking the inner plate to the pump. Now loosen the smaller linkage adjust which is on the outer plate so the rod moves easily but be careful the rod doesn't slide all the way out. Now start the tractor and raise the lift to max height and shut the tractor off with the control still in max lift. Stand on the lift arms and slowly lower the lift control until the pump releases completely. (This should be about halfway down the quadrant.) Now, being careful to not move the position of the control, go back to the outer plate and rotate it so that you can turn control "B" back out of the pump so that the inner and outer plates are again locked together. Being careful to not move the control linkages, rotate the plates counter-clockwise until you feel it click into a detent and tighten the small linkage adjustment. You may have to tweak it here and there depending on how worn your linkages are and I don't recall the adjustments for the traction boost linkage down to the drawbar (and don't use them anyway as mine doesn't have the linkage) but that should cure your creep problem. The control may still creep up from full down to the detent but the lift will stay down. (I normally keep the control at the detent anyway.) One of the problems I had, lack of power, was caused by the pump not developing the pressure it should before the unloading valve popped off (also called a pressure relief valve). It worked fine without a load but could not lift anything heavy. If your's still lacks power after you get the pump adjusted properly, you may have this problem too. I first bought a pressure gauge (0-5000 psi) and installed it at the small port on the top front of the pump where the 'booster gauge' was normally attached. My pump was only developing about 1000 psi, less than a third of its 3500 psi rating and that wasn't enough to pickup even a small 4x4 round bale of hay. You'll have to pull the pump off the tractor (three nuts and two bolts) to access the front cover plate. Four bolts takes the plate off. The plate covers two cylinders, the first one has a the last manual adjustment knob I mentioned above, the rate of lift control. The cylinder without the adjustment contains the unloading valve. Pull the piston out of the cylinder. This is the valve seat assembly which has two o-rings outside and contains the valve seat internally. Watch out for the valve ball as it may pop or fall out unexpectedly. Next pull out the upper spring retainer. Watch out for shims falling off the underside of this retainer. Last out is the spring itself. The spring may be broken or may have weakened over the years, or the o-rings around the valve seat assembly may be leaking. Adjustments are made by adding more shims on top of the spring to increase the working pressure. (If you put shims under the spring, be sure they don't block the off-center hole in the lower spring retainer. A M12 washer works nicely.) Its trial and error here. I doubled the number of shims (a little over a sixteenth of an inch). If it isn't enough, You'll have to pull the pump off the tractor again and add more shims. If its over 3500 psi by your gauge, you'll either have to pull some shims out or be very careful not to hit the end of travel on the rams and blow hoses (at best). Of course your problems may be caused by something else entirely, so get that pressure gauge installed as a first step. Mine was fairly cheap at $20. Good luck.
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