2017 Chevrolet Silverado 2500HD — Transmission & Axle Gear Ratios

Transmission gear ratios

6-speed Hydra-Matic 6L90 (RPO MYD) — 6.0L Vortec (L96/LC8)

Allison 1000 6-speed (RPO MW7) — 6.6L Duramax (L5P)

Available axle ratios

Notes:

• Rear axle is the AAM 11.5-inch full-float on 2500HD pickups. Availability of 4.10 varies by cab, bed, 2WD/4x4, and GVWR package.
• The G80 option adds an automatic locking differential that improves traction at low speeds.

How to identify your axle ratio

• Door-jamb RPO sticker (GM): Open the driver door and locate the Service Parts Identification (RPO) label. On many 2017 trucks this label may also be found in the glovebox. Look for:
  • GT4 = 3.73 axle
  • GT5 = 4.10 axle
  • G80 = Eaton automatic locking differential
• Axle/center-section tag: On the AAM 11.5, a small metal tag may be attached to a cover bolt or stamped on the axle tube. It typically lists the tooth count (e.g., 41-11) or the ratio (e.g., 3.73). Divide ring gear teeth by pinion teeth to verify.
• VIN/build sheet: Use a GM VIN build-sheet lookup (dealer parts counter or Chevrolet owner site) to retrieve your RPO list. Aftermarket VIN decoders can also surface GT4/GT5/G80.
• Physical check (last resort): Safely raise the rear axle, mark the driveshaft and tire, rotate one full tire revolution with the opposite wheel blocked, and count driveshaft turns. About 3.75 turns ≈ 3.73; just over 4 turns ≈ 4.10. Limited accuracy with locking differentials—use with caution.

Towing vs MPG impact

• Lower numeric ratio = better fuel economy. A 3.73 keeps engine rpm lower at highway speeds, especially with the deep overdrives of the 6L90 (0.667) and Allison 1000 (0.61).
• Higher numeric ratio = better towing. A 4.10 multiplies torque more in every gear, improving launch on grades, GCWR feel, and shift scheduling under load—ideal for frequent heavy trailers or plow work.
• Diesel vs gas: The Duramax’s torque and the Allison’s 0.61 top gear pair well with 3.73 for both power and economy. The 6.0L gas benefits more noticeably from 4.10 when running near max trailer or in hilly terrain.
• Tire size effect: Upsizing tires (e.g., 275/65R20 to 35s) effectively lowers the final drive and can make a 3.73 feel like a ~3.42. Consider regearing to 4.10 if you add large tires and tow.

Common issues

While the 2017 Silverado 2500HD driveline is generally robust, owners and shops commonly encounter:

• Ring and pinion whine: AAM 11.5 sets can develop coast/load whine from improper setup, worn pinion bearings, or pattern changes after heavy towing or large tires. Correct with new bearings and precise gear setup.
• Carrier/Pinion bearing wear: High mileage, heavy trailers, or contaminated fluid can pit rollers and races, causing growl or vibration. Fluid service (75W-90/75W-85 with proper GL rating) helps longevity.
• G80 locking differential chatter or delayed lock: The governor-lock mechanism and internal clutch surfaces can wear or stick. Fresh fluid with the correct friction characteristics is critical; severe wear may require a differential rebuild or replacing with an Eaton Truetrac/locker.
• Pinion seal leaks: Common after long towing seasons or vent clogging. Address underlying bearing wear and replace seal; verify vent function.
• Driveshaft/center support bearing (on 2-piece shafts): Rubber isolator tears cause thump or shudder on launch. Replace the carrier bearing and inspect U-joints.
• 6L90 (MYD) harsh shifts or 2–3 flare when hot: Often fluid-related. A full service with correct Dexron-VI and adaptive reset usually helps; internal wear or valve body issues less commonly require overhaul.
• Allison 1000 cooler line seep and spin-on filter neglect: Inspect/replace aging cooler lines; change the external spin-on filter at recommended intervals to maintain shift quality and converter clutch health.

Pro tips

• Always recalibrate speedometer/tire size after gear or tire changes to keep shift schedules and TCC lockup ideal.
• If towing near GCWR often with the 6.0L gas, a 4.10 plus transmission service and auxiliary cooling keep temps under control.

Find a driveline shop on Repairius.