'91 Tercel 5 Speed Manual Problem

Lately when I am accelerating onto the freeway the cars seems to slip out of gear. I'll be accelerating but if I push the accelerator too much, it will rev high but the gears disengage it seems. If I let off and push down a little again it will catch again as long as I don't push down much at all. It seems to me that the clutch plates are slipping or something. Any help?