Didnt all the RPO ZR2 "Highrider" S10's get the 8.5" rear axle?
Looks like 98-2004 ZR2's had the 8.5 as an option at least.
Only 4wd got the rear discs 11.6" x .787" rotors , 2wd got drums 9.5" x 2" .
ZR2's had the 31"x10.50" tires and 3.73:1 gears.
I just found these, its teh SS and Highrider packages.
Super Sport (SS) Package (B4U)
The 2-wheel-drive Super Sport (SS) Pickup is made to order for performance truck enthusiasts. This "muscle truck" is built to haul more than just furniture. The SS package, which is available exclusively on Regular-Cab Short-Box S-Series Pickups, includes the following high-performance hardware:
180-hp Vortec 4300 V6 L35 engine
4-speed 4L60-E electronically controlled automatic transmission with overdrive
New ZQ8 Sport Suspension Package with 46-mm de Carbon shock absorbers, 32-mm front stabilizer bar, 22-mm rear stabilizer bar and two-stage multi-leaf rear springs
16" x 8" cast aluminum wheels
3.42:1 rear axle ratio
Leather-wrapped steering wheel
Body-color grille with halogen headlamps
Red SS emblems and Chevrolet bowtie badges
Red, black or white exterior paint
Rear bumper closeout panel (rear bumper optional)
LS trim (includes YC3).
ZR2 Performance Package
The ZR2 Performance Package is designed for serious off-roaders. This coordinated package of heavy-duty components transforms a 4-wheel-drive S-Series Pickup into one of the toughest trucks in the badlands. The ZR2 option is available on Extended-Cab and Regular-Cab models:
Front and rear track widths are 100 mm (3.9 inches) wider than the standard S-Series Pickup
Ride height is 75 mm (3.0 inches) higher
Extra-wide wheel flares
Unique front fender and pickup box outer panels to accommodate wheel flares
15" x 7" steel wheels with trim rings and black center caps (15" x 7" cast-aluminum wheels optional)
31 x 10.5/R-15 LTC on-/off-road tires
Special frame for wider track
46-mm gas-pressurized Bilstein shocks
28-mm front stabilizer bar
Rear axle track bar
3.73:1 axle ratio
Enhanced front-drive axle with 71/4" ring gear, heat-treated drive gears, and special axles
Enhanced rear axle with 81/2" ring gear, larger wheel bearings and axle shafts
Standard 180-hp LF6 or optional 190-hp L35 Vortec 4300 V6 engines
Heavy-duty 5-speed manual transmission or 4-speed 4L60-E electronically controlled automatic transmission with overdrive
Special jack for added height
Special spare tire winch
LS trim (includes YC3).
So yes, all the ZR2's got the 8.5" ring gear rearend. Same rear as the fullsize trucks and the GNX Grand national.