I dropped the tranny/tcase in my 1990 and am swapping in what i believe is a 1995 tranny/tcase. They are nearly identical with the exception of a sensor and something shown here I believe...I don't have the unit in front of me but this is where I think it was in the pic, what is this???

 

Can't really tell from your pic. Any way you can get a better shot?

 

I wonder if it has anything to do with the switch to electronic speedo's in 92.

 

yeah, in 92 or 93 they switched to an electronic speed sensor.
maybe swap your transfer case onto the new transmission?
if you separate the trans and case i would change the seal at the rear of the trans also.

 

i'm not there now and won't get a better pic till friday, but I don't think its a speed sensor, its a large part roughly 4'' by 3'' and is bolted to the case, looks like some kind of actuator of some sort. I wish I could find a pic of a unit or a part diagram somewhere somewhere.
some type of synchromesh mechanism??

 

Don't swap t-cases just to change to a mechanical speedo - just swap the speed sensors - literally the mechanical one bolts up to the same place as the electronic one.

As far as what you're pointing out - I can't make it out in the pic

 

oh man, I have this same problem!!! did you ever figure out what the mechanism is???