12P GM 3.08-3.90 Dura Grip Limited Slip, 30spl, Composite Clutches. 12P GM 3.08-3.90 Yukon Dura Grip Limited Slip, 30 Spline, Positraction; Composite Clutches. Yukon Dura Grip is a positraction limited slip differential that provides smooth yet aggressive traction, giving you the confidence and performance you need across a wide variety of terrains. The Dura Grip is engineered for long life and is completely rebuildable. Dura Grips are constructed with a high strength nodular case, forged 4320 chromoly spider gears, and composite clutches. For unmatched positraction performance, the Dura Grip is the ultimate choice. When your vehicle demands performance, durability and strength, choose Yukon Dura Grip.