I'm not aware of ANY Tracker ever built from the factory with a steel diff. I've had a '95, '96 a '00 and '02 and all had aluminum front diffs and carriers. The '99 GV with the V6 and manual tranny had the steel housing... not sure of any other Suzuki models with steel diffs unless it was the XL-7s.
I'm going with 5.12 gears on the 1.6 engine manual tranny equipped '96-'98 trucks, 4.62 with the 2 liter manual tranny trucks and 4.88s with the auto tranny trucks 2nd gen trucks.