A833 4 Speed Problems.

Put the car up on jackstands (rear wheels in the air). Put the trans in any gear. Have someone push in the clutch. From underneath see if you can spin the driveshaft (Which will turn the trans and clutch disc) by hand. If it can be turned your clutch is releasing, if it can't be turned by hand, you have a problem. I would start by pulling the clutch apart and inspecting the disc and clutch fingers (do this before you start modifying linkage). Could be a b-body fork (too short), faulty clutch (worn, broken finger pivot, etc.

You can change oil all you want, but it won't fix your problem. All the symptons point to inadequate clutch release.

Also there is a wave spring in between the friction pads on the disc. The clutch pressure plate has to move enough to release the wave spring too.

Someone also mentioned pilot bushing too tight, this is a possibility, but I have never seen one fail like that.