By no means is this definitive, but one could infer from the 2000 brochure below that a 4.10:1 locking rear differential was available with the SR5 "Extra Value Package #5," and a 4.30:1 locking rear differential was available with the SR5 "Sport Package plus locking rear differential." It should also be noted that the 4.30:1 seemed to only be available on automatics, so I would think a manual with a locker would be 4.10:1 and an automatic with a locker could be either. YMMV
-Tim
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