differential says 305 8

is that my gearing? its an '89 two door... and its gutless with 31's...

Probably not. If it's a stick it could be 3.07's. Auto 3.55's. Count one tire rotation versus the yoke rotation(s) and estimate a partial rotation ie...roughly 3.5 rotations equals a 3.55 etc.

What transmission and engine? Or what rpm are you running at 60mph? From those we can make a good educated guess. In addition to any tags on the front or rear diff, you can read the BOM number off the passenger side tube and look it up at http://www2.dana.com/expertforms/deabill.aspx. t http://www.therangerstation.com/tech_library/Dana_BOM_numbers.html has a nice picture of where to find the number on the tube.