Look at your clutch linkage. Start where the pedal attaches to the rod going thru the firewall and down thru to the clutch fork on the bellhousing. Each connection point could be loose or worn and changes every time you step on the pedal. Get someone to step on the pedal while you watch from underneath. If everything looks good then check and adjust your clutch. Set your throw out bearing up as close to the pressure plate fingers as possible without touching them while it's running.