I was researching this a couple weeks ago after installing 5100s upfront on my SR5 4x4. The passenger and driver springs are definitely different, they are side specific. From what I found, the springs on a SR5 4x2 are different from 4x4, and the passenger/driver springs are reverse swapped compared to 4x4. The OEM part numbers are different for 2wd with and without sport suspension (I think this was the XREAS? not sure), and for 4wd with and without KDSS as well as with 17inch wheels, or with 20inch wheels. Anyone can correct me if I'm wrong, it's a little confusing
2wd w/o sport suspension:
Left coil spring #48131-35600
Right coil spring #48131-35590
Left shock #48510-80498
Right shock #48510-80498
2wd w/ sport suspension:
Left coil spring #48131-35640
Right coil spring #48131-35630
Left shock #48510-80233
Right shock #48510-80500
4wd w/ 17 wheels w/o dynamic suspension:
Left coil spring #48131-35620
Right coil spring #48131-35650
Left shock #48510-80507
Right shock #48510-80507
4wd w/ 17 wheels w/ dynamic suspension:
Left coil spring #48131-35650
Strange, but I didn't see a part number for right side for 4wd with 17inch wheels and KDSS
Left shock #48510-80508
Right shock #48510-80508
4wd w/ 20 wheels:
Left coil spring #48131-35730
Right coil spring #48131-35720
Left shock #48510-80499
Right shock #48510-80499