Even if you find out it's the clutch, like LT250RWV said, you are running a ticking time bomb by not running with thrust washers in. I upgraded my stock ones last week with the billet ones and the RM bearing from Mitch. Mostly because I had a blown head gasket and had to tear down anyways. $45 for the washers and bearing is cheaper than a rebuild and I prefer the peace of mind over wondering when the bomb is going to go off.