Engine revs when clutch is disengaged

Hey all, I have a 90 Eddie Bauer Bronco. It is 5 speed and I recently installed a hydraulic clutch. For the past few months I've had a really wierd problem where my engine would sometimes rev an extra 1-2,000 rpms when I disengaged my clutch to shift. I thought maybe the trottle cable was gettin hung but i followed it and messed around with my throttle body and that didn't fix anything. I also changed my throttle control sensor recently thinking I finally figured out the problem but that actually didn't fix it either. It doesn't happen every time but about 60-70% of the time. When it revs it doesn't matter if I let out the clutch again or pump it. It normally just hangs untill I shift or if I wait for it to come back down it takes about 20-30 seconds. I'm really stumped on this one. I was just wondering if anyone else had had this problem or heard of it before. Any speculation on the problem would be amazing. Thanks guys

-Dave