943 lift function has quit working.

The lift function has quit working. The bucket curl still has power. I turned the machine off and started it back and the lift worked for a few minutes , even enough to load a bucket of dirt then quit working again. I did get it to raise to see if the bucket would stay up and not drift down , the bucket set there fine. I'm wondering if a relief has gotten weak or that valve needs a rebuild. Any suggestions would be appreciated.

943 lift function has quit working.