1974 260z I have a clutch that is about 4 years old or so. 110k original miles on the engine

For some time I have noticed some problems with the shifting however today was the worst,

some times when i would take long drives, 3-4 hours on the interstate shifting would seem difficult once getting off the highway. Usually when I am at a dead stop and shift into reverse, it will range from smooth shift, to some grinding, to having to shut the car off to get it into reverse. In the last week or so I have noticed when i start the car in first or reverse with the clutch pedal all the way down, it will creep forward or back on level ground. Today when i went for a short drive I was unable to get it into 1st gear and had alot of difficult in 2nd-4th, each one being a little bit easier. After about 10 minutes of driving I was able to get it into first gear but it was still very difficult, but there was never any grinding on any gears except reverse, it was just very difficult to shift, when the car is off though it shifts with no difficulty into all gears. Some things i have noticed are that sometimes if i pump the clutch for a minute or two it will be easier to shift if i am having troubles, or usually after a few minutes of driving the shifting becomes easier. When I parked the car this morning and just checked it a couple hours later, there were no shift problems except for minimal difficult getting it into reverse.

Ideas?

Try dumping the fluid and rebleeding.