The gears are pretty good. They are beakable though. If the clutch bell gear connection isn't adjusted correctly it can be a problem. You want to get them straight, and as tight as you can, but where they still spin freely. A warn gear, having the spur gear adjustment too tight, or revving the engine when the truck is stuck can be contributors to breaking these gears.
There are metal gears available, but they are heavier and may cause shifting problems, and I'd personally rather have the spur gear break than bust tranny gears, that are harder to get to!
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Shane
Project MadMaXX
www.4x4LA.com/madmaxx/