4. The Gearstar 4L80E Level 3 transmission hovers on the line between street- and race-ready with a unit that will take 600 horsepower and 600 lb-ft of torque. Gearstar replaces every bearing, solenoid, and speed sensor possible. A blueprinted pump and valvebody are added, as well as a TransGo reprogramming kit, a heavy-duty intermediate sprag, and a new roller assembly. The input shaft, main shaft, and forward steel clutch hub are all heat-treated for maximum durability. If your engine is putting out more than 600 horsepower and you think only a TH400 can be built to hold up to that power, think again. Gearstar’s Level 4 package adds a 300M main shaft and 300M forward clutch hub to the 4L80E so it can handle 800 horsepower.