37s on factory 4.10 gears + the 5.7 HEMI is a soft, slow, fuel-hungry truck. 4.56s restore the factory 33"-tire feel — throttle response, low-range crawl ratio, transmission shift points. If you're going 37s and want to keep the 5.7, this is mandatory. With the 6.4 HEMI, 4.30s are acceptable; 4.56s are better.
The Power Wagon comes from the factory with 4.10:1 gears in the front AAM 9.25" axle and rear AAM 11.5" axle. With factory 33" tires, that gives a comfortable crawl ratio and acceptable highway RPM. Bump tires up to 37" and:
Re-gearing to 4.56:1 restores the 33"-tire feel with 37s. The math: 4.56 / 4.10 = 1.112x, which exactly offsets the 37/33 = 1.121x tire growth. Within 1% — you can't tell the difference from factory.
**For the 5.7 HEMI:** 4.56 is the clear answer. The 5.7 needs the gearing back; 4.30 isn't enough.
**For the 6.4 HEMI:** 4.30 is acceptable, 4.56 is better. The 6.4's extra 25 lb-ft of torque masks some of the lost gearing, but for sustained high-altitude crawling or towing, 4.56 is still the right call.
**Cost breakdown:**
**DIY considerations:** Setting up a ring and pinion correctly requires:
If you've never set up a ring and pinion before, the AAM 11.5" rear is NOT a good first-time job. Pay a shop. The $1,200 labor saves a $740 ring & pinion that you'd otherwise scrap from a bad install.
| Part | Vendor | Est. price |
|---|---|---|
| Yukon 4.56 Ring & Pinion Set — AAM 11.5" Rear (PW) | Yukon | ~$380 |
| Yukon 4.56 Ring & Pinion Set — AAM 9.25" Front (PW) | Yukon | ~$360 |
| Yukon Master Install Kit — Front + Rear (bearings, races, shims, seals) | Yukon | ~$580 |
| Professional install (shop labor for both diffs) | local gear shop | ~$1200 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.