At G3 Transmission, we provide general diesel transmission service across all major brands — but when it comes to GM-built transmissions, we go beyond repairs. We are a full-service performance transmission shop specializing in rear-wheel and four-wheel drive GM transmissions across all generations, from the classics to the most advanced late-model builds.

Whether you’re building a street cruiser, a tow rig, a classic muscle car, or a 1000+ horsepower drag machine, we have the experience, parts, and proven recipes to build a transmission that fits your exact needs.

We service and build every GM platform, including:

• TH350 & TH400 – Reliable 3-speed classics built tough for hot rods, drag cars, and restorations

• 700R4 & 200-4R – Overdrive automatics for street performance and retrofits in muscle cars

• 4L60E / 4L65E / 4L70E – Popular in trucks, SUVs, and LS swaps — often needing internal upgrades for real power handling

• 4L80E / 4L85E – Heavy-duty units great for towing and high-power builds, with tons of upgrade options

• 6L80 / 6L90 – Found in newer GM trucks and performance cars — strong cores with the right internals, but common failure points when tuned

• 8L90 / 8L80 – Gen V-era transmissions that benefit massively from tuning, cooling, and converter upgrades

• 10L90 / 10L1000 – GM’s latest 10-speed platforms — tunable, powerful, and complex, but we know how to build them right

• Allison 1000 / 10L100 – Found in Duramax trucks — known for strength but still benefit from billet upgrades and tuning when towing or tuned

Application-Specific Build Plans

We don’t just throw in a shift kit and call it good. We develop tailored build plans based on your setup, goals, and how you use your vehicle. That means:

🛻 Towing & Work Trucks:

• Billet torque converters

• Upgraded clutch packs and steels

• Trans coolers and deep pans

• Optimized shift strategy for loaded conditions

🏁 Drag Racing / Street-Strip:

• Full billet internal builds (input/output shafts, drums, planetary upgrades)

• Transbrake valve bodies

• High-stall converters matched to cam and powerband

• Firm, fast, consistent shifting under high RPM

🚗 Classic Cars & Hot Rods:

• Overdrive conversions for highway cruising (200-4R, 700R4, 4L60E retrofits)

• Period-correct external look with modern internals

• Lockup converters and shift calibration for clean drivability

• Tailshaft mods for custom chassis and crossmember fit

🔥 Performance Daily Drivers / LS Swaps:

• Tuned 4L60E/6L80/8L90 with increased line pressure

• Valve body and servo upgrades

• Converter options for drivability or low-end punch

• Calibrated shift timing for power and smoothness

We know how far each transmission can be pushed — and what needs to be done to make them live. From basic rebuilds to fully built performance units, every GM transmission that leaves our shop is spec’d, clearanced, and tested to match your goals. We use high-quality parts from trusted performance brands and offer options for custom converter stall, billet upgrades, tuning, and cooling solutions.

If it bolts to a GM drivetrain, we can build it — and build it for your exact application.

Let us know your engine setup, power goals, and how you use your vehicle — and we’ll recommend a proven transmission package that gets the job done.

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