how do i check for clutch clearence?

If the push rod at the back of the clutch master cylinder (between cylinder and clutch pedal) pre-loads the master cylinder the clutch will slip, if it has too much clearance it will be difficult to engage gear/break the drive between the engine and gearbox. Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info There is a company that independent auto repair shops "buy" their information from that offer a very reasonable service to do it yourselvers. You can get a one week subscription or year subscription very cheap. The information is year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... great quality information same as the professionals have ,much better than generic workshop manuals from parts stores, much cheaper than the factory manual try http://bit.ly/mitchell_repair_manuals_online and get an online repair manual subscription.

On the Altima, I believe they have one connection for the shaft to go inside the transmission. If the bearing is coming apart, metal can get caught in the internal shifter parts and jam up. Where you hearing any noise from the trans? Why did you get the clucth replaced? Was it slipping or hard to get into gear? If you had just slippage before, the clutch maybe too thick or the slave or master could be a problem. It should be under warranty with the shop that put it in.