I think that Nissan calls the mount that's actually on top of the tranny the rear mount. The one that is at the rear of the crossmember by the shift linkage is called something else. But without checking the FSM I'm not sure. For the above pic, I'm not sure which one this would be, possibly the lower left one? The two on the right look pretty similar (may actually be the same part #, codes are too fuzzy), but the passenger side engine mount and the driver's side tranny mount both look pretty similar as I recall.
I'd actually look at the front dogbone first, when that one is worn, the engine will rock back and forth a lot when you rev it, and you will have some movement in the shifter. This sounds like what you've got going on. Next most likely is the mount at the rear of the crossmember by the shift linkage. I don't think the one on top of the tranny would cause what you are describing.
It's also quite possible the clutch may be having issues as has already been mentioned, unless you pull it, no way to know for sure, but it does sound like something in there may be going out, if not already gone.
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Originally Posted by
lynchfourtwenty It's next to the one on the left
There are only four, they are ALL next to the one on the left. LOL