I just started getting this rattling noise while I was driving in 4th and 5th yesterday and last night it stopped going into reverse all of a sudden. Also, all shifts are getting a little stiffer. Is my tranny about to take a ****?

 

your synchronizers are probably worn. 5th and 6th gear use the same synchro collar so the problems from those two are more than likely related to the shift synchro/collar/fork. usually the synchros go first since they are brass. now is a good and easy time to go ahead and pull the tranny drain plug for a minute. let some drain into a clear cup. take a look at it for gold particles aka brass pieces of the synchronizer. it's an easy way to see if you have worn or damaged synchronizers. If you don't have these gold particles, you can still have a synchro problems, though. As far as your vibration problem goes, it could be many things. When parts are worn or damaged, they can make all kinds or weird noises, vibrations, etc. Technically speaking, the input and output shaft bearings can be a probable cause. it's probably a good time for a rebuild. while the weather is at a low and the car hasn't quit on you all together, this would be a great time. maybe santa can bring you some carbon fiber backed synchronizers and a steel shift fork.