Going with low gears (higher numerically) means your truck will probably crawl over just about anything with greater ease-better yet, it will creep down what's steep with more confidence. Adding a locker makes a uselessly spinning tire but a memory. Both upgrades will bump up your traction capabilities tenfold and will allow you to head deeper and farther into the mud, rocks, and other terrain.
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Why it's good: It has a dash-positioned switch, and when "off," it's essentially a limited-slip. When "on," it's a full locker.
Some features: Its name stands for electronically controlled traction-enhancing differential, so its automatic engagement is designed to be seamless. It can handle C-clip axles.
Available for: AMC 20, Dana 30, 35, and now the 44, Ford 8.8, and GM 8 1/2- to 10-bolt, and 8 7/8- to 12-bolt.
Price: Around $600.
Get it: Auburn Gear, 260/925-3200, www.auburngear.com
Air Locker
Why it's good: Dash-mounted switch plus compressed air means you engage the locker and control traction on demand.
Some features: One-piece nodular-iron differential carrier, heavy-duty solenoid, and patented timed locking system.
Available for: The front and rear diffs of most 4x4 vehicles.
Price: Figure under $800.
Get it: ARB 4x4 Accessories, 425/264-1391, www.arbusa.com
Detroit Locker
Why it's good: Both drive wheels get 100 percent traction. Plus, the C-Locker for C-clip axles and the quieter SofLocker are other spins on tradition.
Some features: It's totally automatic and maintenance-free. Wheel-speed differentiation is one of its talents.
Available for: Virtually every 4x4 vehicle.
Price: $500 to $600.
Get it: Detroit Locker, 800/328-3850, www.eatonperformance.com
4-Spider Traction Lock
Why it's good: Traction is always a good word.
Some features: Manufactured from nodular iron.
Available for: 28- and 31-spline Ford 9-inch.
Price: About $400.
Get it: Currie Enterprises, 714/982-5310, www.currie-rearends.com
ELocker
Why it's good: A pushbutton electronically locking differential that handles like an open diff when unlocked.
Some features: It has a four-pinion design; electromagnets push locking pins into a collar, which locks the axle-side gear into the diff case, performing as a spool for equal power to both front wheels.
Available for: Jeeps with a 27- or 30-spline Dana 30 and many '81-present fullsize Fords and Chevys.
Price: About $750.
Get it: Eaton, 800/328-3850, www.eatonperformance.com
4.88:1 Gears
Why it's good: Low gearing if your Dodge has big tires.
Some features: Machined from hard-core steel; due to the thickness, a notched crosspin shaft will have to be used, but no other mods are required.
Available for: Chrysler 9.25 rearends.
Price: MSRP is $263.
Get it: Yukon Gear & Axle, 800/347-1188, www.ringpinion.com
G2 Ring-and-Pinions
Why it's good: They're performance gearsets.
Some features: Available for the front and rear, they're designed to be quiet.
Available for: Domestics and imports, up to 1-ton.
Price: Starts at $129.99.
Get it: Genuine Gear, 800/269-5903, www.4wheelparts.com
Ring-and-Pinion Sets
Why it's good: Both OEM and aftermarket gearsets are available.
Some features: You can get a used ring-and-pinion if you're on a serious budget, have an older truck, or are looking for an oddball ratio.
Available for: Jeep, AMC, light-duty trucks (up to 1 1/4-ton), Suzuki, and Toyota.
Price: Varies; $188 for Sierra Gear Dana 60 4.56:1 ratio
Get it: West Coast Differentials, 800/353-1513, www.differentials.com
OX Locker
Why it's good: The locker has a four-spider gear design.
Some features: It's made of forged and heat-treated steel, and features a "back cut" gear-tooth style for locking ring and gear.
Available for: Dana 30, 35, 44, and 60, AMC 20, and Ford 8.8.
Price: Starts at $799.
Get it: OX, 877/OX4ROXX, www.ox-usa.com