Micro CoGen.

this is a 1974 tractor and it has a big problem with the 3 point hitch. it use to raise pretty good when first started up but after running awhile it wouldn't raise much.  now it will only barely raise when first started.  after running awhile with bush hog on it goes all the way down and won't raise at all.  when it gets hot it will not even raise the arms by theirselves.   anyone have this problem or know what;s wrong???