The 4.56 gears were available in '89-'95(non-Taco's) and '90-'95 Runners that came with the 3.0 w/31" tires and a 5-spd, they were also in '90-'95 Runners w/3.0 and auto with stock gears. The 4.88's camer in the same years above but were only in rigs with the 31's and auto tranny. I am not sure if the 31's were an option for the 22re's, I have never seen one.

With 32's and the 22re I would opt for the 4.88's over the 4.56's, this would give you better prformance with the 22re.

I wouldn't have an unexperienced mechanic swap my gears, unless he is willing to warranty his work. Setting up gears right takes experience, or the willingness to pull the diffs if the gears are set up wrong and try ity again. I had a buddy who was a mechanic blow 2 sets of gears before finally getting them set right. Bench labor shouldn't be more than about $150/diff to have a qualified shop set the gears.

The $4-600 seems a bit high for used diffs, the front should only be about $150-200, and the rear about $300, unless it is a V-6 rear, or they are set up with lockers.