Is the pinion tight with or without the ring gear/carrier assembly installed? The pinion bearing preload should be set BEFORE the carrier is installed back in the housing. If the tightness happened AFTER the ring gear/carrier assembly was installed, then you will have to re-shim the carrier to the right/passenger side of the differential, as the pinion gear teeth meshed to deep into the ring gear, causing the bind. Any time the pinion nut is loosened up, the crush sleeve should be replaced as that is what sets the pinion bearing preload. If you re-use the crush sleeve, you may shorten the pinion bearing life and ring and pinion life by a great deal. If you have to re-shim the pinion gear itself, then the pinion bearing has to be pressed off a new shim installed to change pinion depth, again a new crush sleeve SHOULD be used.