New Clutch.

1997 Z28 6 speed 95,000 miles

So my car has been slipping more and more in the past few months especially when taking off from a stop and in higher gears at lower speeds. My slippage has been so bad that I cannot burn out on dry pavement and I can hardly accelerate in 5th and 6th gear (the engine revs but the car does not speed up). This and an annoying chattering after I drive my car hard are the only symptoms.

I guess this mean it's time for a new clutch?

Sounds like a worn out clutch to me. If the clutch is original, you would be lucky to get much more than 95,000 miles out of it. Make sure that you replace or at least get the flywheel resurfaced when you replace the clutch, or you'll kick yourself later...