If it were the clutch, you should have a spike in rpms when the slipping occured rather than a drop in rpms.
I would guess one of your sensors (O2, MAF, Cam, Crank, etc.) is going out causing a rich or lean condition in the mix. The only way to tell is to plug it into an OBDII and record a drive to see exactly what happens just before it drops in rpms. It can also tell you what codes you may have even if the CEL has not come on.
Here is a good one that reads PST2 codes and can clear the airbag light too.